You do realise steam, blizzard/battle.net, origin, etc. all use P2P by default to share updates?

Download, yes.

My guess for upload, P2P through game DRMs if OP is centrally located with low latency.

Have you restricted P2P network activity in your household?

My guess is that OP hasn’t turned this off on the game DRM apps like Steam, is located centrally with many other gamers and has low latency. Even if they haven’t bought new games, they constantly update, and then also share those updates.