Vanguard takes screenshots of your PC every time you play a game. Every time you play a game a function is called to screenshot your PC’s screen, in case Vanguard thinks you might have something suspicious, it screenshots your ENTIRE PC screen (all monitors).
Edit: Not trying to spread false info this was shared to me via a friend and there is other data to back up that this is real https://www.unknowncheats.me/forum/anti-cheat-bypass/634974-vanguard-taking-screenshot-pc.html
https://www.unknowncheats.me/forum/valorant/484475-vanguard-screenshots.html
Also any time you open a webpage in Windows, a nude photo is taken of you (whether you’re currently clothed or not) and posted on your mom’s Facebook.
My source for this is the same as OP’s.
Or MAYBE, people who enjoy “hacking” (the actual programmers, not “cheaters”) and go decompile/learn the inner workings of programs might have a better idea of what’s going on? Just a wild guess.