I've noticed in skyrim that sometimes when you look at a plate of food it sometimes shake like there's an earthquake.
Is this a bug in the game??

Yes, as in Bethesda games, their physics engine is a bit weird. For example, sometimes I pick a book out of a shelf or pit up an item in an NPC's house and then everything goes sporatic.

Everything is in constant motion, especially when you're not looking at them. stare at one too long and it simply can't contain itself.