Not an official answer, so don’t quote me on it, but I think “legal entity” is used to denote a corporate body. In this context “legal person”, refers to a “corporate sole”, which tend to be offices held by a single person such as a “Lord Mayor of London” or “Archbishop of Whatever”.
This was better explained in a draft copy of the PSC guidance, but I can’t find it referenced in the current guidance so it may have been somewhere else. I’m guessing the ORP in IN01 refers to the same thing.