Yes, actually. If you had just finished playing a game with that "trainer" loaded.. and then decided to log into Steam and play Rust.. It was most likely still loaded into your memory.. and then that's where VAC picked it up. VAC doesnt care if it detects a hack loaded/in memory that isnt related to or for the game your playing at the moment.. VAC cares that you have hacks at all.
Proof you are lying : Steam does not give "gift cards" If they banned you by mistake they would just remove the vac status from your account and give you somenthing in return *last time it was a copy of left for dead 2 if i'm not mistaken *.They will NOT give you steam gift cards or money. They will NOT refund you and they will NOT leave the vac status if the ban was a mistake. L