Something doesn't make sense.

The WSS (Weight Sensing System) not only determines if the passenger seat is occupuied, but classifies the occupant into one of several categories; large adult, small adult, child, baby-smart seat installed, or unoccupied. This information is needed for SRS to determine the correct threshold/deployment stage when firing the airbags. From time to time, the seat may need to be calibrated to set the correct "zero-point". From your explanation, it appears that WSS was reporting an occupant even though there was none. If this was the case, you'd have had the seat belt warning chime going off all the time, since the car thinks there's someone in the passenger seat who's not wearing their seat belt.

I think the dealer in FLA did the right thing by scanning the system for faults. Keep in mind though, that they'd like to get paid for their time, and MBUSA won't pay for "No problem found". I think they performed the seat calibration so they could cover all the bases on your behalf, and still get paid by MB warranty. Of course, I could be wrong, but I've been down this road many times, each time with the same result. Keep an eye on it, and let me know what happens.