Yes, NT means neurologically typical or average. Ironically enough, "average" only exists statistically and not in living form.
Depending on the website you go to, NT is most often used to describe anyone who is not autistic. However, some people such as myself find this illogical since, as mentioned earlier, not all nonautistics are by any means "neurologically typical". I tend most often to use "nonautistic", or sometimes "NA" (but usually I avoid the latter since many don't know what I'm talking about).
Also depending on the site you go to, it may be used in a derogatory manner, or simply as a neutral label. I think more often than not, given some of the animosity of auties towards the nonautistic world, it's used at least slightly derogatorily, and sometimes downright aggressively.
On average, I would say the population of Wrong Planet does not use it aggressively, mostly either slightly derogatorily or neutral.