I can't believe someone would do that.
The policemen were putting their own lives in danger while trying to save the distraught man. The bag was inflated in case he or a reassure fell.
Such public suicide attempts are selfish in that they don't care they are endangering others.
Whether or not the fellow saw the bag so thought he would be the hero to all probably won't be known. He'll tell the version that best suits him.
I couldn't tell if the crowd was egging on the distraught man to jump, or just supporting the one who was reaching him. There have ben cases where crowds have encouraged jumpers.