Certainly seems odd but it could just be a bilateral rematch clause which wouldn’t be surprising for a fight like this. The media always find interesting ways to report on these things so I wouldn’t be surprised if some of it was embellished and it was in fact a simple rematch clause with perhaps a bit more meat on the bones to ensure there’s no ducking and the loser gets another shot at the belts.
It could also be a case of both camps being wary of losing and wanting to agree on the financials for the rematch so that the winner wouldn’t have more leverage in deciding how to split the purse (or even the venue, date, etc) - they’ve gone for 60/40 to the winner of the first bout for the rematch.
Only way Joshua wins for me though is if Fury throws one of the fights or he gets incredibly lucky. Fury is a far better boxer in my opinion