BQM with router unpowered

Had a power cut at a site without maintained power. An FTTP connection showed 100% packet loss for the duration of the power cut, as would be expected. An ADSL connection to the same site showed some periods of 100% packet loss with periods of lower than usual latency (10ms instead of 30ms) in between. How is it possible to be returning pings when a modem/router is unpowered?

Are both static IPs? If not, the IP for the ADSL connection could have been reassigned to someone else.

In reply to a post by ajseeds:

Had a power cut at a site without maintained power. An FTTP connection showed 100% packet loss for the duration of the power cut, as would be expected. An ADSL connection to the same site showed some periods of 100% packet loss with periods of lower than usual latency (10ms instead of 30ms) in between. How is it possible to be returning pings when a modem/router is unpowered?

It's not. Most likely cause is you're not actually monitoring your router. As suggested, maybe your IP address has changed. This means it may monitor another user. It's also possible that it's being CGNAT where you share the IP with many users. This wouldn't explain it going down though.

Many thanks for your help, both. Should have thought of that.
Yes, the FTTP was static IP, but the ADSL was not, with the router using dyndns.