Discord routes over their own servers and uses a private I3Dnet backbone to spread the signals across the world. The latter is one of the reasons why discord video is very good.
If discord did any p2p there would be stories all over of people getting ddos-ed after joining a voice call / screenshare.
In general, discords tech is pretty solid overall. The platform itself is just getting shittier.
Playtests typically involves a full on NDA for this reason. If your playtest is aimed at creators that are allowed to stream it’s not a playtest, it’s a marketing exercise.