Jesper knows he wouldn't manage to actually touch Kaz's hair, it was a wish but not a likelihood, but he wasn't fully aware of how little he and Kaz actually touch until his wrist is captured. And they aren't touching, not technically, his shirt is in the way, but Kaz is keeping it so Jesper decides to just let him have his wrist. Whatever.

He more or less accidentally stumbled into what was a private situation and one he doesn't fully understand. There's a difference between knowing Kaz likes to put boundaries up between people, and knowing that he physically reacts that poorly to contact. He looks to Inej and then to Kaz, once or twice, frowning.

"Listen, all jokes aside about kisses being good enough to knock someone out, what actually happened? What was it because of?"