A guest at the Vanity Fair bash told People that the singer, 21, and the actor, 30, were engaged in a conversation that looked like more than a light-hearted 'hello'.
'They were outside near the restroom having a discussion,' the onlooker said. 'It seemed a bit more serious – it certainly wasn't a 'Hi, how are you?' talk.'
'It seemed like they were catching up, sorting something out.'
Gyllenhaal, who is believed to have ended things with Swift in December after just three months of dating, left soon after while Swift stayed and partied with her friend.
'They completely kept to themselves,' the insider said. 'She couldn't be bothered by anyone.'