It's not mentioned in the listing description but I see now there is language under the price breakdown that says "this property requires a $300 security deposit. It will be collected separately by the property manager prior to check in." I must have missed that fine print, and this is a non-refundable booking.
I ran it by AirBNB and they said since the host is an "app-connected host" collecting deposit off site is allowed. This is the first time I'vencountered security deposit for AirBNB. I will have to check the property more carefully upon checking in and keep good documentation in case of any false accusations. An extra hassle for sure.
On the other hand, I understand some guests can be destructive, and most hosts just want to run a successful business rather than scamming people. Finger crossed, but I think this should be fine, though in the future I will check the fine prints more carefully to avoid this kinda of surprise.