Why couldn't throwing down food to distract creatures be a skill challenge?XP in 4E is gained through overcoming challenges which are made up of individual encounters. If the encounter is set up as a combat challenge then the foes must be overcome to earn the xp. Treasure is a reward for jumping through the hoops of the challenges.
Throwing down food to distract them to what end? No combat = no xp for the encounter.
More generally - what makes you think it's the GM and not the players who get to determine whether a given encounter is a combat or a non-combat challenge?