WAIT. I know they said he didn’t smell like the caramel, but what if the chemistry clubs caramel had a bit of an unintended side effect they noticed, and it makes it easier to give into certain impulsive behaviours or something. Because while I don’t wanna sound like that other comment, you’ve gotta admit it is a little weird to take a big ol’ whiff of your friend in public, and not even be all that embarrassed by it. And it was audible enough for him to hear it on a crowded train, so you know it was loud.
As for why it only affected her and not him, I don’t actually remember whether he had some too, but they did make sure to emphasise how big he is this chapter. Maybe it’s a matter of because he’s way bigger, the amount of whatever chemicals accidentally caused it wasn’t enough to really affect him. Meanwhile, Chokki’s shorter than average, and waaay shorter than him, so it doesn’t have anywhere near as much area to disperse in and is therefore a lot more potent, leading to sniffer senpai.