In this case, they had no reason to resign unless they counted the points very precisely (I’m ahead by a large margin because the bent four is dead, but it would have been a close game if it had been a seki instead).
It’s possible that they still thought it was a seki when they got the stalling notification? In this case they would have not understood why I “wasted” three moves removing ko threats from my territory, and when presented with the notification they might have believed that I was the one stalling?
Anyway, I was ahead on the board, and they are the ones who passed several times, so I don’t think the anti-stalling mechanism should have triggered at all. My understanding is that the anti-stalling mechanism should only trigger if the losing player keeps playing when the winning player passes. For this game it was the other way around: the losing player was passing while the winning player was capturing the stones.