That doesn’t mean the “they” here isn’t unclear. I wasn’t sure whose Mastodon handle Paul Graham shared. I certainly didn’t think OP meant he shared his own handle.
To be perfectly pedantic, this should only be confusing if referring to the Mastadon employees. Otherwise, if referring to the non-person entity, singular or plural appropriate syntax would be “it”.
They originated around the same time, but singular you was initially only used for addressing superiors/showing respect (using the plural second person pronoun as a singular for this purpose is still a thing in a bunch of languages), a few hundred years later “you” became the standard second person singular pronoun while “thou” fell out of favour.
A very modern convention is now using “they/their” when a person may not be aware of someone’s preferred pronoun. And even still, I have also seen people abandon gendered pronouns entirely.
It's also a very old method. In fact, he/she is a later evolution of the English language. "He/his" used to be more equivalent to "it/its". It wasn't until ~15th century that the modern "he/him" and "she/her" fully evolved. "They/them" meanwhile was in full use by the 14th century
This train of thought makes no sense. The fact that something originated in Old English doesn't at all mean it's dead. He/She also originated in Old English, just a little later. Should I make fun of people using he/him, she/her pronouns because they're "clinging to Olde Anglishe"? lol
It’s also just far easier to use a plural pronoun to refer to a singular person to reflect the idea that you’re talking about their whole persona, brand, work, etc… and not just specifically the human being, IMO.
Paul Graham is a man, not a plural entity.