Remember the oil sensor is NOT operating a gauge, so it doesn't differentiate pressure levels. There are only two meaningful pressures, OK and Not OK, so it's basically a pressure-operated switch. When the pressure increases enough to overcome the internal mechanical resistance designed into the switch, it opens or closes per the design. In this case, your measurements suggest that the controller sees either zero resistance (short to ground) or a resistance of 1.5.
The fact that you see a state change in the oil pressure switch suggests it is working as designed.