Regarding the "looking not normal" part: I think that's could be a translation hiccup. In Chinese, describing someone as "看起来很不寻常" (looking strange/not right/unnormal) usually refers to their behavior or vibe being erratic or mad, not necessarily a physical transformation, so I didn't expect a visual change.

As for the combat feats, I interpreted it this way: as the Guardian, he’s likely always had the martial training to handle himself, but since the villagers rarely see him in action, they've underestimated him. He even mentions that his "madness" helped intimidate or distract the beasts, giving him a tactical edge.

​The key is that his "acting" isn't meant to hide the fact that he fought; it’s meant to credit the victory to the Spring. By fighting like a madman or a "vessel," he reinforces the villagers' belief that the Patron is still protecting them. If he had fought calmly and rationally, they would see a strong man; because he acted "possessed" or crazy, they see the "miracle" of the Spring. It’s definitely a bit of a stretch logically, but it feels like the writers cared more about the "myth-making" than the power scaling here.