Contrail is jet exhaust or rocket exhaust, I assume. There isn’t going to be enough left from the balloon to smoke..
Did you watch until the end? It was smoke and it was coming down steeply from a high altitude. The smoke was very thick in the higher altitudes.
Rocket exhaust could leave smoke but a jet contrail is just water vapor. Plus a rocket’s travel would be over once it exploded not continuing on for miles afterwards.