I mean, he's an asshole, but there's a kernel of validity buried in that pile of excrement.
English is a living language. The way it's spoken in any given area is perfectly valid, and deviation from an origin nation does not matter. American English is just as good as the British version and neither is better than a dialect in a specific area of either country. Nor are any of those more "right" than a dialect in other places.
Formal English is relatively static what with writing keeping it from changing rapidly, but even that isn't better, just easier to use across all other forms as long as formal English remains the default in schools. It's like I tell my kid; you gotta learn formal, grammatically correct English before you can get away with speaking in a local dialect because it's the best way to ensure clear communication. But we can, and often do, use regional dialect freely, and with joy because it's wonderful.
But the jingoistic bullshit the person included in their post is exactly that: bullshit.