Bullshit. The fight lasted maybe 30 seconds and went to the ground almost immediately. Neither fighter was a clear victor. William Cheung didn't get "his ass kicked" in the same way Bruce claimed he beat WJM. It was a pretty pathetic fight by both men. Cheung was around 46 and Boztepe was 24. Some say Boztepe simply ambushed Cheung at the seminar.
There is an edited video of the fight on youtube:
Did either fighter change their style afterwards? No.