Unfortunately Guild Wars 1 is absolutely not a MMO tho.
It's a Singleplayer RPG that offers Co-Op Features through social Multiplayer Hubs. And if we would go by this definition Call of Duty WWII would be a MMORPG, too.
It was Guild Wars 2 was when the Devs saw the Potential of the Multiplayer Features and created an actual MMORPG.