If there is any noticeable movement of the rotor when you grab and yank or work in/out that is a sign of loose/worn bearings. (Not to be confused with the possibility that the steering isn't locked and you are moving both wheels). If the rotor is moving you will feel it, maybe even hear it.
Did the mechanic pop the dust cover off the hub when he "visually" inspected everything? There wasn't any noise when the rotor was spun, but noise when the wheel was mounted and spun, correct?
With the car on a lift, and the suspension relaxed, all of the weight of that wheel was riding on that one bearing.
'73 280SEL 4.5 (9/72)- RIP
Only 8,173 units built from 5/71 thru 11/72
'02 CLK320 Cabriolet - wifey's mid-life crisis
2012 VW Jetta Sportwagon TDI...at least its a diesel
Non illegitemae carborundum.