That appears to be what it came down to. Three players went to the official, one reported, but with three there the official got the number of the one who reported wrong, so the wrong number was announced and therefore the defense did not know that 68 was eligible. Either way you go, one of the teams would have gotten screwed by the official's gaffe. If they had let the conversion stand, then they would have robbed the defense of knowledge about who had reported as eligible and needed to be covered. Instead, they say they announced 70, so Detroit has to adjust for that but it's likely that the Lions didn't notice. That Campbell had told the officials about this play in the pregame makes it worse.