Sadly, “The theme of rebellion against God runs like a thread through the Torah and much of the Bible.” Num 11 presents the next episode of such a rebellion.
The actual episode of a complaint is divided on two sub-episodes: first, people were muttering or complaining (verse 1); and, second, the rabble (asaphsuph) started craving with desire for meat (verse 2).
First response of God was preventive and symmetrical:
Num 11:1 Now the people became like those who complain of adversity in the hearing of the LORD; and when the LORD heard it, His anger was kindled, and the fire of the LORD burned among them and consumed some of the outskirts of the camp.
Important sequence should be noted here:
Complaining people – the LORD heard – the LORD’s anger was kindled – the fire burned.
This sequence describes the future of people who become “like those who complain of adversity in the hearing of the LORD.” First His anger kindles. Second, real fire burns. We are not told if this fire killed any person, but at least, most probably, some of murmurers were injured. I suggest it was a preventive measure, but did it prevent a continuation of further grumbling?
This episode begins with “The rabble who were among them [and] had greedy desire” (1:4). These people wanted “meat to eat.” What does it mean “rabble?” Who were these people? According to the structure of the verse 4 it will be reasonable to assume that they were representatives of “a mixed multitude” (Ex. 12:38) who went out of Egypt together with Israelites.
The murmuring of this mixed group eventually involved Israelites – “and also the sons of Israel wept again” – and even changed the attitude of Moses, “the same Moses who earlier pleaded for Israel’s life, even if it meant blotting his own name out of God’s book (Ex. 32: 32). Now the Lord has two problems on his hands: Moses as well as Israel.”
God responded first to Moses and after that to the people.
The first response was,
Num 11:17 “Then I will come down and speak with you there, and I will take of the Spirit who is upon you, and will put Him upon them; and they shall bear the burden of the people with you, so that you will not bear it all alone.
This response was obviously positive.
The second response was,
Num 11:18 … ‘Consecrate yourselves for tomorrow, and you shall eat meat; for you have wept in the ears of the LORD, saying, “Oh that someone would give us meat to eat! For we were well-off in Egypt.” Therefore the LORD will give you meat and you shall eat.
This response was supposedly positive, however it was supplied with “a fine print,” which added one important detail, “until it comes out of your nostrils and becomes loathsome to you" (11:20). Thus, the LORD warned the people about His reaction to their murmuring and explained the consequences.
Num 11:33 While the meat was still between their teeth, before it was chewed, the anger of the LORD was kindled against the people, and the LORD struck the people with a very severe plague.
Why God’s Responses Were Different?
It is obvious that God replied differently to Moses and to the people. The former was blessed although complained and the latter was punished although it seems did not commit anything unusually bad. Having said “unusually bad” I do not mean that it was good to complain, but it was “just a regular complaint.”
Attempting to answer this question I will suggest to consider two important moments.
First, Moses did not “cross the border.” I suppose that Moses did not complain like other people, that is why God replied differently. However one should keep in mind that later on even Moses was punished for his disobedience (Num 20:12). This fact does not allow to judge or accuse Moses, but rather serves as a red flag to those who would like to test the patience of God.
Second, and more important moment is people’s accusation. Moses’ complaint was a cry for help, “Num 11:13 “Where am I to get meat to give to all this people?” whereas people’s complaint implicitly accused the LORD in their hardships,
Num 11:5-6 “We remember the fish which we used to eat free in Egypt, the cucumbers and the melons and the leeks and the onions and the garlic, but now our appetite is gone. There is nothing at all to look at except this manna.”
In fact, these words meant: it was better to be slaves in Egypt than to be free with the LORD.
These two moments at least partially explain the consequences for Moses and for the people.
Of course, it is very easy to suggest how one should behave in such a situation, but incredibly difficult to demonstrate own perfect example.
 W. Gunther Plaut and David E. Stein, eds., The Torah: A Modern Commentary, Revised; Accordance electronic ed. (New York: Union for Reform Judaism, 2006), 950.
  Scripture quotations taken from the New American Standard Bible® (NASB), Copyright © 1960, 1962, 1963, 1968, 1971, 1972, 1973, 1975, 1977, 1995 by The Lockman Foundation Used by permission. www.Lockman.org.
 Walton, John H.; Gane, Roy; Block, Daniel I.. NIVAC Bundle 1: Pentateuch (The NIV Application Commentary) (Kindle Locations 48912-48913). Zondervan.