This has happened three times now, at different NPCs in the quest, some miles from the stray dog spawn, which is past coincidence, imo.
Basically, due to the nature of the quest (having to kill mobs, lots of competition, people getting bored / selfish wanting to do it asap), and the fact that a load of 220's are doing it, people are training the stray dog spawn to the NPC, wiping it to generate the adds and then leaving them at the NPCs.
Of course, if you're level 220, you won't get aggro from them, leaving you free to continue talking to the NPC / getting the missions. However, for the level ranges intended, this is both deadly & prevents you doing the quest.
Can I suggest the stray dog spawns have leashes please? (I know this is probably a one off case of abuse by one person, but making them less deadly all around would be a great thing, imo )