@Cristina2190 It's weird that this seems tied to your credit card.
Airbnb does gave an algorithm that detects bookings that are statistically most likely to result in unauthorized parties. The factors are under 25 years old, living in an area local to the listing, booking for only one or two nights, and booking an entire home listing.
Simply assuring the host that you are quiet wouldn't have any bearing on this algorithm kicking in, because the host has no ability to overide it.
Also, hosts have reported that guests are getting this message even when the booking doesn't fall within those algorithm factors, so it's obviously glitchy.
All I can suggest is that you contact Airbnb for an explanation.