It does, don’t remember the details but at one point I let a packet capture tool on my phone run for a few days and checked which apps phoned home. Gboard was one of them. You’d besurprisesd at the amount of network traffic for most apps between 2-4 am.
Just remove its network permissions, and it works fine (without the phoning home part) AFAIK other spell checkers / autocomplete aren’t quite there yet
The massive influx of new ratings could also simply be linked to the fact that the game is included in this month’s humble choice, adding a ton of new players