Who’s responsible after basement flood

Hello!

First time posting and I’m looking to get some help and opinions after the basement of our apartment flooded. A couple of weeks ago our basement began filling with water coming from underneath the baseboards and flooring on one side of the basement. We promptly notified our landlord, and the whole flood and damage to walls and floor was repaired in about a week. We were told that cracks in the foundation contributed to the flood, but that a human caused clog in the main drain leading to the sewer was the main issue. We have only lived in the apartment for about 6 months, and are pretty careful about what we put down the drains, not flushing anything other than human waste and throwing out used cooking oil, not pouring it down the drain, and using a mesh screen to catch debris in our kitchen sink. I have once put about half of an old container of sour cream (500ml) down the drain after mixing it with hot water and soap (not the best idea I know, and now I just throw it straight in the garbage). Our landlord now does not want to reimburse us for not being able to use the basement, and is heavily insinuating that we caused the clog. I didn’t get a chance to speak to the plumber when they were fixing the issue. I was wondering if this could be the case and that bit of sour cream I put down the drains screwed us over majorly? We live in an old duplex in a major city, and our half of the duplex is split into two apartments, with another tenant on the top floor and us on the main and basement levels. I’m not sure if the main drain is shared with the tenants on the other side of the duplex. The issue took place right around the rainiest time of year for us, with lots of days of rain leading up to this issue. I had also noticed shortly before the flood that our basement toilet was not filling correctly, with it not filling very much at all after flushing, and even draining some water when not flushed, though it would flush normally. Any thoughts would be greatly appreciated, thanks!