Any chance that's where a cat (or possibly a dog) likes to rub against the wall or walk extra close to it while going around that corner?

The spot looks dirty, and I was thinking the same as the post above. A cat or dog rubbing on the wall when going around the corner. As to the texture, I suspect its always been there, and you are noticing it right now, because it is looking dirty. The wall may have been textured at one time, and someone had a thin skim coat put on it, and now that skim coat has rubbed off in that one area.

Before I saw the 2 previous posters comments I thought exactly what they thought. Do you have a dog? If so it is a good possiblity the dog is rubbing the wall while walking through that area.

I have spots like this around my house from the dog leaning on the wall. Wash it with a bit of dish soap in warm water. The lanolin in their coat resists water so a bit of dish soap helps.

Thank you all for the comments/suggestions.