The crashing snowspeeder scene seems like another "ANH grappling hook"-type false memory.
If that is the case then this could explain it:
a) There is a shot of a snowspeeder coming towards the AT-AT almost head-on, seen from inside the cockpit
b) There is a shot of another AT-AT's head exploding
c) There are shots of damaged speeders flying uncontrollably
d) We do not see what happens to the last AT-AT
With the fate of the last AT-AT unexplained, I would imagine it is quite possible that one's mind fills in that gap with elements that were seen.