I was living in an older home with an unfinished basement that flooded several times. The dining room floor is located above the basement.
I had a brand new rug over the dining room floor and when I removed it to clean there was a dark blackish spot about the size of the bottom of a round trash can. There were no stains on my new carpet from pets or any water/liquid spilled.
The new tenants after me also had a rug on that floor and now there are multiple spots throughout the floor; some darker than others.

The landlord is trying to sue me for over $1000 in damages. I need some advice on what could have possibly caused this. My initial thought was moisture in the floor or leakage from the basement yet no water was present. Could it be mold? What are my options? Any input or advice would be greatly appreciated (no I don't have a picture unfortunately). I've hired an attorney but I'm trying to gather additional information. Thanks so much for any input.