Your proposed meaning is a more recent interpretation. Searching online I see the mysogynism angle becoming more prominent in the 2010s: https://pursuit.unimelb.edu.au/articles/how-neckbeards-have-...

here's from stackexchange from some years prior: https://ell.stackexchange.com/questions/3173/whats-the-non-l...

https://metatalk.metafilter.com/23545/Neckbeard-is-this-a-wo...

I've seen it use as a synonym for "unix beard". https://dilbert.com/strip/1995-06-24