Good question! We used KataGo to score the games*. KataGo's notion of pass-alive territory is quite restrictive: it's territory which is guaranteed to remain alive even if one player keeps passing and allows the other player to keep playing stones in that territory. The formal definition is points 4 and 5 under the Additional Definitions heading of KataGo rules. If we look at https://goattack.alignmentfund.org/?row=0#no_search-board then the white territory in lower-left is not pass-alive: if white passed indefinitely, then black could surround the stones and capture it.

* With one exception: the results against hard-coded baselines were scored by the baseline script itself, so that we could also evaluate against other AI systems like ELF/Leela on a level playing field. We tested the scoring for that agrees with KataGo.