Carb ice. Of course, I wasn't sitting there with you so its just an arm
chair opinion. You say the carb heat worked as advertised but did you
turn it on?

Fuel venting. I'm trying to remember how a 152's fuel is vented. Is it
vented caps or a venting tube? It could have gotten a bit plugged by
dead bugs moving around. If you havent' already, I would remove the
caps and blow air into the tank to see if there is any restrictions.

Great job of handling an uneasy situation with professionalism.

-Robert, CFI