Some nerds or geeks are incels. Some nerds and geeks aren't incels.

Then some incels are geeks or nerds, but not all incels are geek or nerds.

Honestly, to be a nerd you only need to like certain things. And some of those hobbies help to socialize. For example: LARPs or CONs. And wait for it, some people hook up at those events. XD