I'm sure they just all slipped and couldn't keep fighting after his fist touched their head right! Not his power.
Vitali was never known for power. He couldn't drop a lot of fighters he faced. The volume of punches he landed did the job.
Accumulation KOs still require power, you're being beaten in the face with a blunt object until you get KNOCKED OUT. this does not happen 41 times without power, despite what 100x undisputed undefeated seasoned professional fighters on forums tell you.