Repeating the exact query I used last night with the same pair of MAC addresses this morning, the location returned has altered at the 7th decimal of precision so it seems it's a (near?) realtime process updating the MAC database with the GPS locations from the phones/tablets.
For several years google maps "satellite" imagery has had a reasonably accurate position for my postal address, but since they updated the imagery a few weeks ago (it shows my new lawn) they now think my address is four houses along and on the wrong side of the street, so 1/4 inch of precision for the MAC address, but 100 yard accuracy on the map!