I think his point is that DNS doesn't require the TCP or HTTP overhead.
There are more steps and layers involved with an HTTP GET and reply than with DNS resolution.
It requires TCP overhead if the dns packet is bigger than 512 bytes. You could abuse the DNS protocol to carry HTTP-esque metadata but it would be a small victory over standard HTTP. Reusing an existing TCP connection is more efficient.
TCP is not required for larger messages if EDNS(0) is available--which it probably is--and the network allows; which conservatively, it probably does at least till the 1280~1450 byte mark.