According to Dave Meltzer on Wrestling Observer Radio, before he went out for his confrontation with Kevin Owens that ended Smackdown, Vince McMahon created a wound on his forehead and the covered it up with either Nu-skin or Vaseline.
Then, after taking the headbutt from Owens, the cut reopened and he bled on TV, which was the plan for the segment.
Meltzer also stated that the plan was for Stephanie McMahon to come with a towel to clean up the blood, but that was aborted.