That is an overstatement. There are several motorcycles that are "oil cooled" BWM R1100 and 1150 Boxer engines the older Suzuki Bandit 1100 and
600 come to mind. Both are complete with oil filled cooing jackets, jets, and oil filled radiators. We also know that in all engines the lubricating oil also serves a cooling function. Another example of oil cooling can be found in turbocharged engines both gasoline and diesel. This would be the oil jets that are aimed at the underside of the piston crowns and fed by the pressurized oil gallery. Cools the piston crown.