@Laura2592 I wouldn't consider asking for someone's number to be universally unacceptable. If the other person was underage, or they'd been in a workplace situation, I'd find it problematic. But a crush on the Hot Neighbor across the fence sounds pretty innocent - it's just awkward when they're "ballsy" enough to involve you in it but too shy to just ask his number directly.
I was uncomfortably in the reverse situation once. Staying in an Entire Home property with husband for a long weekend in an exciting city we'd been dreaming of visiting for years. At check-in, the hosts (a gay couple) explained the rules and reiterated that "you can't bring anyone else here, unless it's us!" I didn't think much of it until the next day, when they sent a nice message asking how everything was and if we wanted to join them for a drink. We thought they were inviting us to go out to a fun local bar, but eventually they clarified "wouldn't it be more fun to do it at your place?"
The interest wasn't unflattering, but I did find it a bit odd that Entire Home hosts would invite themselves over to their own apartment for Sexy Times. Unfortunately we didn't reciprocate the interest, as we wanted to get the most out of our holiday and not feel obliged to entertain the hosts who we were paying for the Airbnb. But perhaps for some other guests, a spontaneous orgy in a 17th century loft would have been the highlight of their trip - so I politely declined and made no mention in the review.