There have been a few very brief (a few seconds) power blips in my
area over the past few weeks (perhaps half a dozen such outages) and
one sustained outage of about 3 hours.

I don`t think these count as being off supply - payments are normally
only triggered by an outage of 18 hours or more afaik, BICBW :-}

If you`re back on within seconds, its likely an auto-recloser switching
back in (they normally switch about 3 times before they lock out)

The longer outage might then have been to do post-fault maintenance on
the breaker, depending on its type, or to get someone onsite to reset
the auto-recloser.