They've been spoofing numbers for quite some time. It only stands to reason that randomly generated spoofed numbers will be numbers belonging to other owners of phones. They think they're being clever about it: use the same area code and exchange numbers as the target, and randomly generate the final digits, hoping you'll think you know the caller and will answer.
I actually use this to screen calls because my exchange and area code are from T-mobile in Pierce County WA circa 2003 and I've long since moved away from that area.
The strategy falls flat when calling a cell phone, but seems to make a lot of sense when targeting landlines. A call from "someone around town" seems worthwhile to pickup.
Add in the fact that people with landlines are more likely to be older people whose priors expect a human to be calling, and the only real question is why don't the spammers catalog and then exclusively target landline prefixes with this method.
It seems like ILECs could start offering a service based on ingress filtering source addrs based on numbers they know haven't been ported out, but Ma Bell is the antithesis of innovation.
I get robocalls "from Quincy, Mass" on my iPhone which has a Quincy number. I haven't lived there in 7 years and have no genuine interaction with anyone there.
