On Steam? Using ViGEmBus? I'm wondering if you are seeing inputs for multiple controllers, the Quadstick and the ViGEmBus virtual controller.
I don't have that game but most game properties in Steam look the same.
In the game's properties-controller look for Generic Controller being enabled. We don't want that if using ViGEmBus.
In Steam's general settings, disable Generic controller support:
Once that is done and the game is restarted, if you are still seeing unexplained controls, turn off QMP program and see if the quadstick by itself is producing any response from the game. If so, the next step would be to install HID Hide and set it up to hide the quadstick from any program except QMP.
It is also possible to disable Enable Steam input for both XBox and Generic controllers and just map the controllers inside the game's internal controller settings.