It's just that the ghost of my 5th grade English teacher would have emerged from the mists to point out that "they" is plural, whereas I was referring to an individual. Can't win.
Words mean what people who use them intend them to mean.
But if you want something more authoritative than random-internet-comment, definition three from dictionary.com has you covered:
https://www.dictionary.com/browse/they
they
pronoun, possessive their or theirs, objective them.
1 nominative plural of he, she, and it.
2 people in general: They say he's rich.
3 (used with a singular indefinite pronoun or singular noun antecedent in place of the definite masculine he or the definite feminine she ): Whoever is of voting age, whether they are interested in politics or not, should vote. A person may apply only if they are over 21. They have been an actor since childhood.