It is evidence against such an explanation, but it's very weak evidence. It shows other factors are involved, which no one disputes, but it does not rule out genetics as a factor.

Incidentally, your Q&A argument is incomplete. We have data which shows accent is not genetic - correlation between the accent of genetic parent and child is gone if you look at adopted children. If there is a twin study on the topic, I'd give 1/p value of the study odds that identical twins raised apart have minimal correlation of accent.

In contrast, identical twins raised apart have a 75% correlation in intelligence and adoptees have a 25% correlation with genetic parents. (I'm working from memory here since I don't have the book with me. The numbers are far from zero, but might be 70% and 20% or 80% and 30%. http://www.amazon.com/Genome-Autobiography-Species-23-Chapte... )

The source you cite is simply being dishonest by leaving this part of the dialogue out of his conversation with a straw man.

Also, your source has a very different philosophical basis for knowledge than most people. He believes that aggregate quantities (e.g., pressure, temperature, possibly g) are statistical myths. See here http://news.ycombinator.com/item?id=2210600 , which is a response to http://cscs.umich.edu/~crshalizi/weblog/523.html (which he cites in the article you link to).