He hadn't expected that the guy, who didn't seem very talkative, would bombard him with a string of questions, leaving him somewhat overwhelmed.
Especially the part where he said, "I'm not very good at optics," and then proceeded to ramble on with a bunch of questions, which made him feel a bit embarrassed.
The most important thing was that there was a delicately pretty girl from the School of Mathematics there.
As everyone knows, as a university student with aspirations, it's not a big deal to lose face in front of a bunch of brothers. But if a beautiful girl is mixed in among the brothers, that's a different story.
Even by force, one must save face.