Negative Life
When the other person had negative life, the game didn't end. Maybe they had a card that prevented it, but that would seem odd.
1
vote
BohnC#64207
shared this idea
-
LarterStyles
commented
Gotta read the cards. They had Herald of Eternal Dawn on the battlefield (https://gatherer.wizards.com/FDN/en-us/17/herald-of-eternal-dawn), which clearly states "You can't lose the game and your opponents can't win the game."
Therefore, as long as they have that creature on the battlefield, reducing their life total to zero (or negative) has no effect.