I think your example (the one before the highlighted area) cannot be used as a comparison. The only way this example would be relevant is that if the OP had put their items in such a way that it impedes these people's passage to get to or from a location. And if that's the case, then, I agree, they should be able to move it to the side and walk over. But this is not the case, the OP's belongings were on/around chairs and these people moved it away so they can use the chairs. I think the highlighted part would be closer to a comparison, and as you mentioned, you wouldn't be allowed nor, most likely, even consider doing such a thing.
You did not understand my example. People have claimed that the simple act of touching someone else's stuff is rude and is the basis why they cannot take the chair. I show there are perfectly reasonable times to move someone else's stuff when it is very clearly correct to do so. The only question is whether the chair is saved or it is not. If the chair is not allowed to be saved then the original occupant's stuff is in the way of someone else and they can rightfully move it out of their way.