I don't think that's right. The interior finish is an even coat which has been aplied to all but the mating surfaces as you can see in the photos. It is not just an exterior coat which has been applied to some of the interior. Further, I very much doubt BMW are incapable of isolating the exterior surface when paining it!
Regarding how to deal with the blisters, I think your idea is a bad one. If you scrape away some of the surface then you lose the integrity of that surface and allow oil and heat to penetrate under the remaining surface via the hole you have created in that finish. Same as if you chip the outer surface of exterior paint - unless you reseal it, it create problems.
In any case, I'm just documenting what I did and why. If you encounter the problem, I have no doubt you will deal with it as you see best.