pretty simple: snowman goes in powdered snow block and stays there for a while because the pathfinding sees it as a block you can walk through. snowman dies a slow, cold death. usually, you would expect mobs to avoid these, but more importantly, snowmen should be immune to frostbite. did the pumpkin add so much life to the snowmen that it caused them to die from frostbite?

also, I am someone else using my dads account.