In Big fights like that a lot of the penalties are enforced as coincidental penalties. Both guys go to the box, but the teams still play 5 on 5. In this case, the one extra guy probably started it so got the extra penalty. Maybe it was a double minor or a major, so longer than two minutes.
After the first whistle after two minutes on the coincidental penalties, they all get to come out. But the one guy who didn’t just get a coincidental must have had to serve more than 2 minutes for the initial call.
let me know if I’m understanding your question right. I didn’t watch that game so just going off your description