The distinction that is missing here is that “they/them” has always been used as a non-gender specific third person singular pronoun to refer to an individual in the abstract only.

What is new and grammatically confusing is that we are now using those pronouns to refer to specific individuals.

It’s a small distinction that makes a big difference .

The following tweet/joke from Titania McGrath proves the point:

“My non-binary friend Steve is often misgendered by bigots who like to pretend that gender-neutral pronouns can cause ‘grammatical confusion’.

They are upset with them because when they call them him they are disrespecting their right to choose their pronouns for themself.”