The space was comfortable, clean, and close to the metro. The apartment had everything we needed for our stay.
It seems as though the host may own rentals in the area and asked for a rental agreement and credit card number for damages that might occur. Any damages can be reported to Airbnb, so you should never provide a host with credit card or any personal information. The rental agreement seemed like a general document, and we just assumed it was for visitors who rent space outside of Airbnb.
In all, this was a lovely place to stay.