I'm almost certain it was a Swans fan as it was immediately followed by Swansea fans shouting shush.
And I also thought the City reaction was worse. You don't show outrage at a minutes silence being broken by chanting 'you jack bastards' during it, even if it's in response to someone/some people not adhering to it.
Both clubs have their idiots, but for what it matters, I think it was started by a Swansea fan and ended by City fans.