@Kenneth12 As I'm sure you're aware, there are many places where thievery is rampant. Here in Sayulita, many hosts who rent out entire places or even some with private rooms, have extensive security systems, cameras, motion detector lights, etc. It has nothing to do with spying on the guests, but to detect thieves getting in. There is many a tourist here who arrives, checks in, relaxes for awhile, has a few beers, showers, dresses and goes out to dinner, sometimes even neglecting to properly lock doors and windows,- they're in "I'm in paradise, I checked my brain at the door" mode. Then they come home to find the place has been broken into (even if locked) their money, camera, etc, gone. The thieves are clever and watch the homes and see when a taxi arrives and drops people off with luggage. Then they bide their time.
Pretty clueless host for sure who thinks he can just run his business in a lackadaisical way and collect the money, and likely didn't realize he had to disclose the camera. I'd just leave an honest review, and send the host some strong private feedback about his hosting style, letting him know you considered reporting the undisclosed cameras to Airbnb, which would get his listing shut down, but that you preferred to give him the opportunity to correct his listing. Then maybe check back in a few weeks to see if he has actually added this info, if not, flag and report.