Fury v.s Ngannou?

Sources say that an agreement has been made for a fight between Boxing champ (WBC) Tyson Fury and MMA champ (former UFC) Francis Ngannou to fight on october 28th in Riyadh, Saudia Arabia. What I dont understand is that they will be putting their championships on the líne. I dont see how, Ngannou never boxed profesionally and Fury has never been in the cage. The sanctioning bodies have rules. I figure it might be a conmemorative belt which most likely be a made up WBC belt like in the Mayweather v.s Mcgregor fight. That aside it will be a massive fight to see who the baddest man on the planet is. Although lets be honest the only way to prove that is to fight one fight in boxing and another in mma or even better with no rules. This goes to prove that boxing is a bigger draw than mma, thats why promotors have them box in the ring and not fight in the cage.