True. Its all about cold fuel icing. Since the MD has a "wet wing" the fuel is in contact with the wing skin panels. When the airplane has been flying, the fuel gets cold. As the fuel burns, the remaining fuel pools close to the wing root making that section of the wing very cold.

Even high humidity can tend to form ice/frost on the upper and lower sections of the wing. Often that ice cannot be seen, hence the "pole check."

A secondary reason for the check is to keep ice from shedding during the takeoff roll into the engine intakes. Most MDs have heated wing blankets that warm on the ground and prevent the upper wing ice from forming. That said, some companies will require a pre-departure ice check to be done by either the flight crew or ground maintenance even with wing blankets installed.

It is also possible that their wing blankets may have been MELed, requiring the tactile check.