Jet was a fucking dumbass. For all he knew, iroh could have been a waterbender. Water benders can heat up liquid too.
No scene in cinema will ever top the reunion of zuko and iroh. That was such a powerful and heartfelt scene that words cannot describe. its the climax of zukos personal arc. The culmination of all his decisions, mistakes, lessons and growth. It is the final beat of a series long redemption arc. It is what most filmmakers wish they had