Well spotted! Like the other answer explains, the + includes people who lack a gender/sexuality/romantic disposition.
Since the best way to fix confusion is by an edit, I've been talking to another mod and we propose to edit the tag usage guidance to:
Use this tag when issues specific to lesbian, gay, bisexual, transgender or other sexual/gender minorities impact the interpersonal interaction in the question. Don't use it when a member of the LGBT+ community is involved, but them being LGBT+ isn't relevant to the question.
Right now, The LGBT+ wiki so far only includes when to do/don't use this tag, but that info is supposed to go in the tag usage guidance: The tag wiki is supposed to be a general introduction to a topic defined by that tag. They're a place to consolidate and form a sub-community around a tag. They contain, among other things, frequently asked questions in the tag, top users in the tag, and best recent answers in the tag.. Not a list of when to (not) use a tag.
I propose we edit the tag usage guidance to the proposed sentence above and clear the tag wiki until someone proposes a proper one. (This is status-completed on 18/03/2020)