A friend with a '96 Accord LX automatic was parked facing downhill, turned his car to ON, didn't start it, stepped on the brake, shifted to D4, let go of the brake, rolled downhill to about 25mph, mashed on the brake and stopped. (This was all inadvertant of course).

After this incident, his check engine light came on, and his mechanic reported that his transmission has "internal damage" and would only last about 6 months more. Right now, when the car is cold, the tranny misses the 1-2 shift (during the shift, revs go up, but car doesn't accelerate). It didn't do this before.

Could that incident have been the cause of his transmission troubles and why?