No, a two month old post certainly isn't necroposting. That was odd that your post disappeared, not sure what happened there. We do prefer that people add to existing threads, even old ones, rather than start a million different conversations on the same topic. On very rare occasions a problem arises when someone, most usually a brand new member who is (sorry to all you responsible TFOLs out there) at the younger end of our age range, comes in and brings up a very large number of old threads. If they were actually adding new content, that would be a very different thing, but the hypothetical poster is simply adding one line, or even one word, responses. The implication is that they are not really trying to participate in the conversation, and perhaps they are simply trying to inflate their post count (for some reason this seems important to some people - I know, I have the largest post count, so I guess I'm king of the world in their eyes). The negative here, as noted above, is that this can push newer topics off the front page. This would be frustrating if, for instance, you just posted a new MOC but got no feedback because your new thread was displaced by twenty old threads. In a backlash to some past instances of this, there are some older, grumpier members of the forum (casting the first stone at myself here, as I am both old and grumpy - Get off my lawn!), who become prickly at any sign of necropostery. Anyway, I think the key thing I was trying to emphasize at the start of this thread is that there is a happy medium. Necropostery is not, in and of itself, a bad thing, but should be done in moderation and with an eye to enhancing the conversation.
There are some old topics that will particularly raise hackles. The whole gray/bley thing was really contentious and people spent a lot of time fighting about it. Some people left forums and even the hobby over this. Most of us have found a way to live in the world as it now exists (some of us only use the older shade, some have switched over, some mix the two colors), and would rather not have the same fight all over again. I forget the term, but someone made up a word that was even more cumbersome than 'necroposting' that basically meant 'dig up the dead horse only to beat it all over again'.