I know that, when if you read the texte it's always spelled "Rollston" (which the spelling I also read in every book). I believe there is a typing error in the title in that Coachbuilt page.
EDIT: I just re-read the page and O.Puzzell is right. The company began as Rollston, then another was formed and named Rollson in 1938. If this car is Rudolf Bauer's car as I guess, it was built by Rollson, without a T.