Yes, this is INT-INT, even if Schengen immigration is cleared at OSL. The Schengen agreement is an agreement between independent countries, and travel between these countries is still international, even if passports are not required.

OSL has three separate parts: DOM, INT Schengen and INT non-Schengen. Basically: customs regulations are more important than passport control! You can buy tax-free goods when travelling to a Schengen country, but not to a domestic destination.

When arriving from non-Schengen countries the plane docks at the far end of the INT pier, where the non-Schengen gates are located. After passing through passport control (i.e. entering Schengen) one enters a long landing leading to the escalator down to the arrivals hall. All Schengen arrival gates leads into this landing, thus one technically is in the INT Schengen part of the terminal. On this landing, the INT-INT checkpoint is located. After passing this checkpoint, one walks down the stairs to the INT Schengen departure hall. Arriving from EWR one has entered Norway and the Schengen area, but one has not crossed the Norwegian customs border, and will usually not be checked by Norwegian customs officers until after the arrivals hall.