There may be others that have heard different, but from someone in the room when the ACC offered (and showed me a pic they snapped in the conference room at the LA Coliseum when Swofford officially offered), they'd said "we'd see people from the ACC at academic events all the time. We knew conference expansion was going to come back so we maintained the relationships."
I'd also heard that the first offer was going to be SU and UConn but, led by BC, there was little support for bringing in UConn, so SU was asked who they wanted to come with, and that's what led to Pitt.