Here's the explanation I got from a long-time P5 RO:
This is consistent with the theory that replay can rule on touching by an ineligible player when that player can be identified BY NUMBER (50-79), but not by POSITION (e.g., a "covered up" receiver). The latter has, of course, never been reviewable, and is enshrined in the case book.
So, when we are talking about an otherwise-eligible number in a 2 X 2 formation, this follows the "BY POSITION" from above, and I support the interpretation. People have been asking me for months if this was reviewable, and I have been telling them pretty much what the interpretation says -- not reviewable, but if the officials are down there struggling with where the receiver came from, a voice from up above might be able to help them.