Especially if Steam isn't willing to shed absolutely any light on it.
I have my suspicions about the ban, but I'm not completely sure.
Remember when the first Fallout 4 mods started showing up, way before the creation kit? Well, a mod (place in red) used Cheat Engine to function, so I'm guessing that.
The ban is for TF2 by the way (hadn't played any other game in the category at the time when playing Fallout 4). So no more TF2 VAC servers for me.