This sounds like an ‘act of God’ - which is not your fault. Insurance is to pay for occurrences such as this.
Do not allow residents to put their problems on you. While you do need to investigate and cure any power surge problem (and/or call the electric utility to straighten it out), your residents are responsible for having renters insurance for accidents exactly such as this.
The only exception would be if you knew about the problem and willfully ignored it. But you are clearly not that sort of person, or you would not even be asking the question in this forum.
So encourage your resident to file a claim with their renter’s insurance company, or encourage them to get renter’s insurance if they don’t have it. But now that you are aware there is some problem with the electric lines, do what you can to make certain it never happens again.