re: Possible but it seems unlikely
IIRC they did say in the press conference that the heat from an impact could last for thousands of years. The temperatures average out to not much below zero already so residual might melt the ice for a long time. The fact that they can only sees these things in craters obscures whether or not the crater impacts themselves are involved the the formation. If we could drill down outside of a crater we would then know if this was formed from the crater heat or not.