So I watched the video and it sounds like they were also using a website to determine where Pokemon were appearing. Reading the Vice article the quote “and that they were only monitoring a tracking application to catch mythical creatures” appears.

I mention this both because I find it interesting. The phone app will show you Pokemon nearby, but if you’ve caught the Pokemon before you can only see in your immediate area (the immediate area is wider for rural areas, but hardly enough). They also seem to know exactly where each Pokemon who pops up is, with more accuracy than you would get from the phone app and likely further away from where they were.

And the second reason is that, while the video proves plenty, I assume they were using their car computer to check a Pokemon tracking website. I would bet the start of this investigation came from checking the logs on that device.