We don't know what is written in this contract, mostly we never will know either, so nobody can tell you if there is a breach or not, but i doubt it.

Having in mind that mindgeek is a very smart company and and the "exclusively" part was mentioned only by verge while mindgeek said directly
they can imagine in some time to add other cryptos as payment too, i'am believing mindgeek here that it's no way exclusively.