In my city and country people use a certain site to track gyms, raids and all spawns. They know where and when which mon is, how good it is (IV) and just drive around catching one after another. Within 2 weeks of the 2nd gen III wave i already saw a 3600 slaking in one of our gyms…
On top of that people then have a whatsapp group where they report the insane spawns like a wild 3k cp Blissey or the 100%'s
One of my team instinct mates hunts 100% IV pokemon this way. To each his own. I’m not proud of it but i tried it once last spring for 2 days and got bored of it so fast fast i quit the game for 5 weeks, no fun in hunting that way IMO.
Now i just use the site to track gyms and raids.
So to sum it up: people can easily have good mons that fast.