The same happened to me last week. I did not have a tight connection from a BA domestic to an AA long haul but during the flight the CSD told me what was going to happen. So on the air bridge I was met by two BA staff and with one went down the steps on to the apron where a van was waiting by the plane. Then a pleasant drive over to T3 - very sociable driver. He then escorted me to the BA Lounge - saying the AA one was useless (although I find the Flagship Lounge OK). No security checks an all in all it took about 15 minutes.

A very pleasant experience. I got the feeling it was an occasional Gold perk and nothing to do with tight connections. I also suspect it only happens with OW connections.