You don't need a special Oregon license simply because it is a Class A rather than Class C. You might need one for other reasons, but I doubt it as long as the coach is for personal use rather than commercial.
There may have been confusion over the terminology, since Oregon uses "Class C" to represent the standard, non-commercial, driving license and "Class A" is one of the Oregon commercial license categories. These do not
equate to Class (Type) A & C motorhome use.
Per the Oregon.gov website on Oregon Class C licenses:
With a Class C driver license you may operate:
-Any motor home for personal use, regardless of the weight of the vehicle or combination of vehicles. Motor homes for personal use have not been included in the definition of commercial motor vehicles in ORS 801.208 and, therefore, operators are not required to possess a commercial driver license.
2004 American Tradition; 2014 Buick LaCRosse
Homebase in the Ocala Nat'l Forest near Ocala, FL