You think your misunderstanding is caused by how Pfhrea formulated their first comment. When they say "I use singular they", they meant they want people use t

You think your misunderstanding is caused by how Pfhrea formulated their first comment. When they say "I use singular they", they meant they want people use this pronoun to refer to themselves instead of he/she, because (I assume) they are non-binary (ie. neither man or woman). They don't expect you to use the singular "they" other than to refer to them. And that's not too hard to remember, you already have to remember whether everyone else is a "he" or a "she"; allowing for "they" is just an extra bit. And if you do forget it, it's ok, just don't do it on purpose.