"Trolling" to me means pretty much means looking to start a fire fight. It has more to do with the intention of the poster than any sort of exhange of ideas or opinions.
So, if a thread has been dead for months and someone brings it up. And the instigator from eight months ago feels the need to throw in another shot, that's "trolling".
(Funny, wonder where I got that "hypothetical" from???
Whether or not someone responding to the afformentioned dig qualifies as "trolling" or not--well that's all in the eyes of the each individual poster who comes across the thread. I can think of at least one poster who believes that it would be.
The really funny thing is that he somehow never seemed to note that the instigator took another dig. He didn't just post.