Using the plural pronoun for a singular meaning is actually very common in English: the originally-plural ‘you’ got extended to mean a formal, singular ‘you’ and ultimately completely annihilated ‘thou,’ and even ‘we’ can be used as singular if you’re pretending to be the Queen or Helen Mirren.

But then, in the late 18th century, grammarians started recommending that people use ‘he’ as a gender nonspecific pronoun because ‘they’ was ostensibly plural, as part of the grand tradition of awkwardly shoehorning English grammar into Latin which has caused many of your present grammatical insecurities, and which I’m totally sure had nothing whatsoever to do with the patriarchy.