I thought of it as Chan glancing at it, then immediately freaking out without being sure, if that makes sense. It's right next door to the office supply store, but ofc most people would actually look to confirm the location before calling. Chan is quick-tempered and controlling, so he saw that and immediately assumed FL was trying to cheat on him since the sex shop is rumored to be a hook-up place for men.

Like a lot of abusive partners, Chan doesn't like FL to be places where he 'shouldn't.' That's why he's constantly checking and obsessing over FL's location and harassing him over it. It's not really logical because it's not something a mentally-well person would do.

Hope this was clear! Thank you for the message!