I think Fussy satisfied my curiosity. I had missed the call. Curiously, I got a similar call from another number (281-933-1429) within an hour or so. That may be the biggest coincidence possible, but this is the third or fourth time a similar thing happened. I'm not sure it should be a pattern, but I'm putting it out there, in case others notice something similar.

The number they called is a cell phone, therefore illegal for them to call. Nobody ever gets that number but real humans with whom I actually have some kind of relationship, so there is no Existing Business Relationship possible. Robocalls are illegal.

I think Fussy is right, but I'm not going to block the number so I can actually catch (And, hopefully, record.) the operator in action if they ever call again.