One section of the wall isn't exactly as smooth as the rest. It has bubbles of paint forming on it that can be rubbed off. They very tiny. The walls aren't dry wall and the section that is I'm question used to be a window.
I didn't do it myself. But what I know is, remodelling old painted walls. It was prepared and painted two coats of new paint. The unique part of this section is it was a window or opening for old AC unit. The old paint showed clear cracks around the frames of old "window" showing that previous painters were unable to repair the wall.
Now I'm facing something similar maybe with the tiny bubbles. I asked around and people dismissed it as a problem, said it's just cosmetic feature.
Best Answer
If it's concrete or plaster applied to brick, that's a porous surface, which can lead to bubbles like this if not sealed/primed beforehand. At this stage, you could treat the paint itself as your (rather expensive) primer coat. Basically the wall has now been sealed with paint instead of primer, so you can sand it smooth and paint a final coat on top. As long as you don't fall prey to the other things that can cause bubbles (all user error, not product issues) then you should have a smooth finish.
Those you asked are likely correct that this is nothing more than a cosmetic issue. Other more serious concerns (excess moisture, etc.), would likely manifest in a more obvious way than just tiny bubbles in paint.