Yeah, I think there are two Steves, with one still frozen until about 2011 in that alternate past.
They set the rule about time-travel when they go to the past they can only change history of that reality (or dimension), not the original one.
It seemed like they broke that rule at they end though when older Steve was sitting on the bench. He would have had to have found a way back to the original dimension to be able to be there. For instance he rebuilt the time-machine with the help of Hank Pym or Tony Stark from that dimension. Which is stretch and a lot of trouble just to be able to give Falcon the shield.