Is he actually choking? (not moving air, not making noise, turning blue) Or just gagging? Gagging is a natural part of starting table foods that most kids go through as they learn what size bites they can handle. Gagging is a good thing because it happens when they get a chunk too big and causes them to spit it out. DD gagged a lot for the first 2 weeks or so of solids where DS rarely gagged at all.
He gags, coughs then starts choking and turning bright red....sometimes he vomits and sometimes (rarely) he swallows it.