if they are here to change the fundamentals(without no valid reason and without any needed improvement, like the 21M market cap) that made bitcoin great then they are clearly making an altcoin, that's how i see it
ETA1: Re: "Hearn created an altcoin with XT" was never accurate: (to an extent that it mattered, as its pulse was gone before the discussed forced fork date that I don't even know to have or not ever been coded).
ETA2: Don't mistake my use of the name Hearn for confusion as to who Gavin is. Gavin provided coding support for multiple alternative clients, but he did not create them and I don't know whether he personally publicized him using his name (vs letting the creators do so).