u/johnsonstein17 explained it pretty well
I am not big fan of nascar and I am not really sure about what is going on but from my knowledge, after you cross the finish line you do one or two more “victory laps” just to celebrate and go back to pits where the celebration goes on.
The winner ran out of the gas while doing the victory lap and everyone else probably already passed him.
Other dude stopped and pushed him around the track to help him, other wise I am pretty sure they would bring out the safety truck or something like that and tow the car back into the pits.
Again, I just watch nascar crash compilations and everything that I am saying, I am pulling out of my ass and knowledge from other motosports.