I assume that people don't usually get Muna in the middle of the fight, yeah. The world is generally not super different for NPCs in regard to stuff like that and IF has made numerous references to people gaining Muna or other benefits after fights they've been in with us, so I'm pretty sure it does indeed work that way.
And why would he put on an act? He'd allow himself to get trapped in place in order to...what? Make people hoe could already demonstrably hit with his total result of over 1000 not defend as well? Like, there are two options here:
1. This guy is green as grass and not lying.
2. This guy has no need to lie so why would he?
Like, this critter's dice pool is such that him lying is surplus to requirements unless he has a huge weakness like the one just demonstrated.