This happened to me twice, I can try to find the other moment if needed (it was during the damage phase the other time). But basically I think you get the screen to scroll when he's on edge of the screen and he just leaves the screen for an insta-kill.

I wonder if that could be it actually. I didn't even notice the screen scroll during that fight lol. I'll try replicating it tomorrow evening

I came to the same conclusion while messing around with it and practiced it for a bit and managed to get it first try on two different attempts. One attempt probably being the fastest it can be beaten at 4 seconds for the fight (timing: Wallop to Knockout)

Way faster than eight-ball by a good 6-7 seconds with WSG.

Tried this this morning, if the cards are a match then the monkey will still go off screen but it won't die so you have to restart the fight. Probably not too dangerous in a run but it felt like it was worth mentioning.