I always wondered this myself. But, Conor used to be SBGi's boxing coach there and Conor has trained his boxing at the best gyms in Ireland. He trains with a TKD instructor too that he refers to as "Dragon". Then of course with Gunnar at SBGi and on occasion when they go train at Mjölnir. Owen Roddy is one of his coaches that has trained him for over a decade and is his primary padman.
The others don't look nearly as good with their striking but they also don't have the boxing background that Conor had, where he had great teachers (not trainers, teachers, like two-time Olympian Phil Sutcliffe Sr.) for a while as well as Paschal Collins, former pro boxing WBO Middleweight and WBO Super Middleweight champion Steve Collins' brother (who was a former boxer himself and even has trained Steve). So, Conor has boxed at the Crumlin Boxing Club (CBC) and at the famed Collins' Celtic Warrior Gym.
Conor did do some semi-contact kickboxing early on but I'm not sure where he did that at. He's trained with a lot of well respected coaches, at least in boxing he has.