I find this on the internet, though usually reddit rather than here. I am forever asking folks if they mean the US, and trying to explain to them that there is... a rest of world
America is the largest (primarily) English speaking community in the world and both Reddit and YC are US companies. It's not surprising some assume the whole audience is American.
The US accounts only for about 10% of English speakers in the world.
Honestly it's kind of hard to know what the audience for a site might be. If people are active during your hours and in your language, the assumption is easy to make.
Oh boy, do I hope we don't talk about the US in 2021, anymore. It's been like a slightly different, ever the same car crash you drive by, every day. For four fucking years. I am sure my dopamine receptors look like old, all dries up raisins by now. I wish we as a species could agree stop all news for year or ten. Detox and heal, form new habits like life has value and shit.