It relates to the whole RDFa vs Microdata argument, which itself is being used as a proxy for the W3C vs WHAT-WG power struggle. RDFa is the W3C’s solution for embedding meta-data into HTML, whereas Microdata is Ian Hixon’s baby. The W3C working group recently voted to split Microdata out of the HTML5 spec, something that Hixon, as editor, was not pleased about. He did it for the W3C spec, but not for the WHAT-WG, thus meaning the two specs are no longer in sync.
Whoever is right, Ian Hixon’s opinion should be only be considered in light of his personal stake in this issue, and his often demonstrated disdain for the W3C and its processes in general. Portraying the W3C as a secretive, compromised organisation helps to drive people toward the WHAT-WG. Of course, the WHAT-WG, being a smaller, invitation-only group of browser vendors, is in many ways more opaque than the W3C, it just lacks some of the bureaucracy around it.