Indeed.

I said that because my only knowledge about OBEs is what I read by William Bulhman.
In his book he say that in his OBE that the astral worlf is a little bit different than the physical world.

for example some objects in his room will be different, not there or other stuff will be here.
Then how can he be sure that he is not dreaming? since he never confirmed seeing something while OBE-ing that was in the physical world without him previously knowing about it?

However yes, if you indeed witness something during an OBE that can be confirmed later you were really out of body.
But I won't believe until it happens to me