That would explain it, 60Hz / 50Hz * 33 1/3 = 40rpm. It seems to be a synchronous motor so it would need a different pulley. The adjustment range is supposed to be 6% which isn't enough, and is done using their split pulley arrangement (I have the CS505 which is similar). It might be worth trying to set the adjustment range to see if it can be used to change 50 to 60Hz (if its a toothed belt arrangement the belt may be able to be repositioned to change the range of adjustment).
It isn't. You'll definitively need another pulley that is designed for 60 Hz operation.
The pitch adjustment works by a cone that is driven between the six pulley segments from above. If this cone is fully out, miminum (- 6%) speed already is achieved, as the pulley's effective diameter is at it's minimum then.