The guy on the right was apparently not paying any attention and started shoving the other guys bike. Then, when he realized what was going on, he continued to push the other guy rather than change his course, figuring the other guy would get out of his way instead. They got caught on each other, the guy on the left got pulled off his bike, and kicked it away to keep it from harming his legs. When the guy on the right finally stopped the guy on the left had had enough and punched him for being an ass.
Edit:
Found a short article on it:
https://deadspin.com/motorbike-racers-crash-into-each-other-pull-over-star-1833553507