I think that's actually 65/80 not 75, but as others have mentioned, 52 is too low to keep the sensor light off. Chances are, the dealer used the reset tool after rotating the tires, but once the PCM figured out the air pressures, it tripped the TPMS again.

The reset tool simply resets the wheel position within the PCM allowing you to move the rear tires to the front and the front to the rear when rotating. It doesn't allow you to reset the TPMS or override the TPMS in anyway.