Hm, I'm not sure about that. Gurkinn had no problem with giving you the Mega Ring, and even said that he would have given one to all of you if he had had that many to give. And he seemed to be both in contact and on amiable terms with Prof. Sycamore, at least judging from his dialogue. Plus, Korrina and Sycamore both recite the same things as being necessary for Mega Evolution (they both mention the Mega Ring, a Mega Stone, and a strong bond), so as far as knowing what's required for the process, the two are on equal footing. What Sycamore seemed to be looking into as the "mystery" of Mega Evolution was what exactly that "bond" was, and why there were "examples of Mega Evolution found only in the Kalos region," going off of what he says in Coumarine City. The post-game seems to give him the answers to both of those questions, with the "bond" being human emotions that are transmitted to the Pokémon via the Key Stone, and examples of Mega Evolution being found only in Kalos because Mega Stones were created when AZ used his weapon to ravage Kalos.
In fairness to them, Sycamore only even mentions Mega Evolution on four occasions, and one of those is just him saying that it's what he and Lysandre were discussing. The other times, it's his initial pitch at his lab, and then explaining a bit more about the mysterious elements of it at Coumarine City (which is after you've received the Mega Ring), and then finally in the post-game at the Anistar Sundial. So it's not as if he was constantly going on about how super-duper secret it was all throughout the first third of game. He just played it up as a big mystery when he was first explaining it, probably in order to get the Kalos Pals interested.
