This is additional evidence that the newly discovered object is the 3rd stage from one of the Apollo missions. They were painted with titanium oxide paint.

The article states that preliminary measurements show a rotation rate of once every 63.5 seconds or once ever 127 seconds. They're trying to pin it down more accurately. That's a pretty fast spin rate but it might be explained by outgassing (or explosion) from residual propellants. Several upper stages, especially those with cyrogenic propellants, have exploded in the past due to residual propellants. This causes a lot of space debris. Current technique calls for the user to vent the residual propellants after the burn is finished.