I think I can answer why you went thru passport control
In researching a soon to occur trip to Poland, I found a website that stated that Poland and Iceland are now part of the Schengen group, thus this was your first point of entry into Europe and therefore pass control. This is just like what happens when one connects in Amsterdam to points East.
Good report and looking forward to the rest. Too bad that you did not book an Iceland stopover since Iceland is really an interesting place.
Also NW solicits contributions via onboard announcements for "Air Cares" as similar program.