How is at-fault party determined in a home fire? I am a tenant, and the landlord's insurance is subrogating for him.

There was a fire in my apartment while we were out. We came to know about the fire later from our landlord, who left a voicemail. The neighbors had called 911, and the fire dept. came and it turned out that there was smoke emanating from a vessel on the stove. Damage was mostly smoke (no actual fire), but landlord's insurance covered the claim (they say in the tune of $7k).

There was a power outage that day for 5-6 hours, and we were out of the house the whole time.

I got a letter from the landlord's insurance that they think I am responsible and want to know my insurance info. I didn't have renter's insurance, so I'll talk to them directly.
My question is: how can they claim that I was at-fault? I wasn't at home, and there might be a malfunction in the stove due to the power outage!