Some games do not allow mouse and gamepad to be used at the same time. Since vorpX often has to emulate a mouse for head tracking, it has a built-in gamepad to mouse/kB emulation that can deal with such games. The alternatives in such cases would either be no gamepad or no (mouse emulation) head tracking.
Contrary to nieda‘s reply that is not a problem, it‘s actually the solution to deal with games that otherwise would not allow to have head tracking via emulated mouse input and gamepad input at the same time.
You can freely configure the gamepad mapping on the input page of the vorpX menu. You can also disable it entirely there (X-Box Gamepad Override). Just be aware that whenever this option is enabled per default, that is usually the case because otherwise the aforementioned conflict would occur when a game does not allow mouse and gamepad input at the same time. So disabling it only really make sense if you don’t care about head tracking.