Because the parent comment stated "Yes, the basis for the hypothesis is fried chicken -> black people and craft coffee -> white hipsters" as if it were a matter of fact. The blog post makes no mention of skin colour at all (that I can see) and the racial connotations are entirely those of the parent - hence injecting racial bias.

I spent one sentence (the middle one) out of the three sentences in my reply explaining why I thought it could be (please note, "could be", as in, I did not say it was, as in, I did not accuse) interpreted as such. My reasoning was perfectly explicit and plain.