People for some reason think that Thor was bruised by this stone pillar.
This is based on nothing but an incomplete assumption.
If you actually watch the scene, we never actually see Thor's face until after Ultron hits him
This means that there is no evidence at all that Thor was actually bruised by the stone.
The rumor started simply because somebody lied about what happened to lowball him, or got it incorrect, and for some reason the myth stuck.
The closest we get to seeing his face is this frame, but there is nothing on it that was not already on it before he was hit.