Personally if guests did that in my home. I would have asked them to leave. Their behaviour is outrageous and could have cost you a regular guest and YOU are worried about getting a bad review from them? @Melanie686
Absolutely follow up with them in person to ask why they did this, confirm your conversation on Airbnb messaging and leave them and honest review and rating.
Also flag with Airbnb.
I would refund your regular guest for his night in the dirty bedroom.