I used "Contact Host" and was still booked. Steps
1) Enter dates
2) Pick Place
3) Pick "Contact Host"
4) Host says place is as available
5) Get message from AirBnB saying I've been approved by host
6) Get message from AirBnB saying host has charged my card
At no time did I pick "Request a Booking". I thought it would stop at #5 and I'd have to then login to AirBnB to finalize the details but no, the host was able to do that without me even though I never picked "Request a Booking"