Listen at 13.40, he mentions that although first funding came from YC they didn't go through a YC batch - Patrick had previously been a YC member with another startup: "Auctomatic".
I mention the merger here in a series of Viewpoints for the BBC: http://news.bbc.co.uk/2/hi/business/6701815.stm
Also, the outcome of Auctomatic: http://news.bbc.co.uk/2/hi/business/7315598.stm