Chongo went into plenty of detail, so I won't (thanks, Chongo!)
But more simplistically, yes..."disproportionately" is the key word here. There is a line where luring goes from a sound tactic to a cheat or an exploit, especially with the game's AnsI (Artificial not-so-Intelligence) being what it is.
I have seen people taking half steps with their characters until the one closest NPC in a spawn group notices him when another NPC in the same spawn just a few feet away remained oblivious...and then repeat this for the whole spawn. I've also seen people lure creatures back to some of our unkillable NPCs. These types of things definitely cross the line. These aren't the only examples.
So if it feels like you're getting away with something, you probably shouldn't do it. If you have a question, ask a GM. We'd rather take the time to watch or answer questions instead of disciplining them or banning them.