Maybe it had something to do with his... vision impairment, but Matt made some assumptions and snap judgements about the people he talked to and corresponded with. When Jean first offered to help him, he... wasn't sure what he was expecting, if he had been completely honest, but it certainly wasn't a teenage bug whisperer with hair a different shade of red compared to the world around him showing up outside his door.
Though they didn't really talk about themselves, Matt understood her on some level. Blind guy trying to make it through school and passing the bar didn't stand a chance of completely fitting in. Always a blind guy, never just- a guy. Not sure what to do with his extrasensory abilities, conflict between the principles his father wanted him to live by and the devil that his mentor had brought out from within him, torn between letting bad things happen to good people and doing something about it - her state of mind would have been a strange kind of familiar.
He might have dwelled on it longer if she didn't do what she had just done to help him with his infestation. One eyebrow crawled up towards his hairline as he tried and failed to mask the fleeting look of surprise on his face.
"You didn't kill them all did you?" he asked with a small laugh that seemed genuinely impressed and slightly uncertain.