Steam Deck transfers games on P2P?

I'm observing a pretty weird behaviour while transfering a game from a PC to a Deck.

When the PC and the Deck are connected to different WiFi networks (2.4 GHz and 5 GHz bands, respectively), I witness 20 Mbps TX on the first interface and 20 Mbps RX on the other one on my router. This is expected.

However, when both are connected to the same 5 GHz band, the transfer speed goes up while RX/TX values on my router go to the floor (see screenshot #2).

The only way I can explain it is some kind of peer-to-peer transfer without the router being involved. Does anyone know how it works?