What did they say about Hashem?
Radak: "Can He set a table in the Midbar?" This was in their hearts, like "Dibarti Ani Im Libi", "Amarti Ani b'Libi" (Koheles 1:16, 2:1). They did not say so with their mouths, that they request meat to test Hashem, and not due to need.
What is the question "ha'Yuchal Kel La'aroch Shulchan ba'Midbar"?
Radak: In a place where there is no food, can He set a full table with all needs of sustenance? He gave some things needed for the table - manna and water, but can He set a full table, with meat? He brought manna from Shamayim, just like snow and hailstones 1 , and water - many rocks, water exudes from them. However, from where will He bring meat?!
Malbim: Can He set a table not lacking anything - bread, meat and water? Even though He already gave meat [they asked if He can give all three at once - refer to 78:18:2:2. - PF]
Even though snow and hail are merely frozen water, and are not food, they did not consider manna to be so different from them. (PF)
