Challenge in the past used to air Brainiac of all things, so airing something like My Kitchen Rules isn't entirely without precedent. And the Wrestling, though that was more likely to be because Sky closed Bravo, launched Challenge on Freeview and didn't have anywhere else to put the wrestling so presumably it was a contract thing.
Yeah, the wrestling couldn't go on any Sky branded channels due to their WWE contract. So when Bravo was shuttered, they could only have put TNA on either Real Lives, Pick, or Challenge. Challenge was the best fit.