[alephnerd]

Your point is correct, but because this is HN, I'm going to be ridiculously pedantic and correct 2 statements in your example.

> The Chinese of Thailand often cannot speak any Chinese (they speak Thai)

That was because of forced assimilation in the 1930s-50s by their proto-Fascist dictator.

> Yiddish is a Germanic language spoken by a non-Germanic people

Because there was plenty of intermarriage and the community was in Central Europe since Roman times

[bradrn]

I think that is their point. Languages often spread by processes unrelated to genetics.

[thaumasiotes]

In the case of Thailand, the same political forces pressured the Chinese into intermarrying with the Thai, so genetics do come into play. But a clean victory was won over language; that didn't happen with genetics.

[canjobear]

These seem like explanations, not corrections?