I would guess they simply recorded the packets they captured on the various WiFi channels as they drove by and processed all the data at a later time.
There’s a difference between sitting there and waiting for networks to identify themselves while scanning all the channels (the software you use). This is a drive-by where they capture whatever happens to be going on at the moment while briefly present.
If you can’t be bothered to minimally secure your network on the public airwaves then you have no right to complain that others are capturing what you’re broadcasting. I might add the the frequencies involved are unlicensed public frequencies.