They could also have been practicing with a simulation of the review process using real-world app submissions for a while before this, and gotten the experience from that.
Imagine you write a script which creates a spammy app (eg. no content, 100% ads). You launch on the play store, and instantly insert a few 5* fake reviews, and then for the next 10 minutes you do a heavy ad blitz all over the internet and other mobile apps to get a decent installed base.
All those users now see what 'appears' to be a brand new app, already getting decent reveiws! They install it, only to find it's junk. Many won't bother to uninstall, so the app maker gets to keep popping up modal ads and running a background service for years...
Repeat the whole process 20 minutes later with another procedurally generated app on a new account...
https://arstechnica.com/gaming/2019/03/a-dev-trained-robots-...
An interesting tidbit is that their ads had 27% click-through rate. They believe it was due to the games were much better than whatever the ad was showing, so people clicked it to get away.