You can't even remap the toggle fullscreen bind.
He means the keys on the keyboard are acting up.
You aren't looking for Blockland settings. Go back and turn off sticky keys.From what I gather sticky keys has 'stuck' alt and possibly shift. When you hit enter, it is the same as alt-enter (fullscreen toggle).
If it's going fullscreen when he's pressing enter, he's holding down Alt when doing so.