Indeed, when I create a Facebook event, there's no field offered for tagging or categorising an event.
If a event is created by a page, one could presumably chase down the category of the page. However, they're fairly non-specific: the kind of page we're looking for might be
Companies & Organisations -> Computers/Technology,
Websites & Blogs -> Computers/Internet or simply
Other -> Community, and any of those are going to catch lots of things we're not interested in.