There are several online dictionaries of emoji meanings.
The intended meaning of [math]unicode{x1f60B}[/math] is “Face Savouring Delicious Food”, which is the Unicode name of the emoji.
U0001f60b Face Savouring Delicious Food Emoji (Emojipedia) offers “Used to indicate a silly happiness; goofy; hungry.”
U0001f60b (Urban Dictionary) offers “thirsty; desperate”
Face Savouring Delicious Food Emoji (Emojibase) notes that :yum: is used in some phones as an abbreviation.
A Google perusal suggests that the “food” association is prevalent.