Why would I agree with that?
The thicker (higher viscosity) of an oil, the slower it will flow.
The lower the number the thinner the oil is. If it’s just one number on the bottle (30, “straight 30” it’s only been tested at one temp (210) and never tested at a lower temp.
Lets go even to room temperature. A straight 50 oil vs straight 10 oil, which would you say is thicker?