It might very well be chambered in 30-03.
A standard 30-06 round will chamber in the above and the operator wouldn't know the difference,,just assume it's a 30-06.

Not a lot of 30-03 loose rounds rattling around in most peoples misc ammo boxes to allow checking to see if it would accept that one or not.

A chamber cast would tell you but I don't know if that was done,,not a lot of descriptive info with the listing.
Neat rifle though. Looks like a Mannlicher Schoenauer sporter trap butt plate.