Toilet overflow damage

[Michael Nahm]

My tenants live in an 8th floor condo I own. It appears that they used the toilet, it got clogged and began to overflow. It seems that the tenants did not notice the issue and left out of town. 

A few hours later, the buildings’ maintenance team get a call from a resident a couple floors down regarding a leak from the ceiling.

The maintenance team unclogged the toilet and did what they could with the overflowing water.

I’d like your opinions on whether the tenants are liable. The maintenance team says that the tenants’ caused the damage, thus insurance should be called. 

My question is whether I should get the tenants to contact their renter insurance policy (I’m not certain they got it, although the lease does stipulate it explicitly). 

Thank you all for any useful advice.