You assumed wrong.
Downloaded game fresh from Steam. Put Steam in offline mode. Downloaded current trainer from site. Right clicked run as admin on trainer. Ran game. Got to main menu. Disabled network adapter. Game clearly shows internet disconnected. Pressed F1 to activate trainer. Trainer Activated. Clicked continue game. Once again game shows disconnected from internet. Clicked Launch. Game started. Activated unlimited ammo and no reload. Demonstrated options.
Trainer working fine in OFFLINE MODE as intended.