Coyote Breath-You are right of course, that IS an anorak, but this side of the pond the name has extended to a certain kind of person, usually but not exclusively male, who is boring, obsessed with obscure trivia and minutiae.

I think the term nerd probably about covers it.

I think it came about due to the prevalence of the anorak as a garment for train spotters, twitchers, and the like.