@Gwen386
Yes, it's possible that the host was using more than one platform, but even if they were only using Airbnb, this can happen if they use instant book.
The way that it works is this:
Booking request trumps booking enquiry.
Instant booking trumps booking request.
However, all the units in the area doubling in price within a few hours is very, very odd indeed. It does sound like the host decided to decline your request because they realised they could get more for the same dates.