You probably hit the kill limit. Was it TDM? Because if they guy already had 25 kills in a row, that's already giving his team a lot of kills. Add in all his teammates' kills and the nuke itself and it probably reached the score limit.
EDIT: Really, the nuke always ends the game? Does it always result in a victory for the person who set it off, even if their team has less points?
Is that how they get around the problem of radiation?
Nuke ends the game, your team wins, no matter the score.
There's even a challenge in elite challenges called ultimate sacrifice, specifically for calling down a nuke to win the match when your team is losing.
The nuke on it's own is rare enough, and if you're 25 kills in a row, your
team is probably already crushing. I can't imagine this ever happening, but it's technically
possible. Probably more likely in domination since you can get a lot of kills but still be losing.