The wedding was between staffers Brian Mosteller and Joe Mahshie and took place at the Naval Observatory, the Vice President's official residence. The couple specifically requested that Biden officiate, reports BuzzFeed News. It was his first time officiating a wedding so he got a temporary certification to make it legal.
Biden has always been ahead of the curve on the issue of gay marriage. In 2012 in the run-up to Obama's re-election, the VP announced his support for legalizing gay marriage, putting pressure on Obama to declare his own support shortly after.
In short: coolest uncle ever.