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.