Well that's not the one I talked about. The incident I have referred to happened some years ago and as the Concorde was filmed by a cam installed outside the balloon there wasn't a 30,000 feet height difference either. It looked to be on the same level and VERY near. It was only visible during a few video frames. Actually you could use this to estimate how fast it went by. As they were obviously not prepared for the event and I don't think that the outside cam was zooming (you could see part of the balloon in the same picture) and you could see Concorde's shape pretty well, it must have been REALLY near.
Anyways it must have been an incident to remember. Therefore I hoped that someone might have some first, second or third hand information.
To give some more information:
The balloon flight was one of four or five identic gas balloons starting in the USA. The winner would be the first balloon crossing a European street. The effort was initiated by a balloon manufacturer (looked british but might have been american too). The capsule design was closed and painted yellow. One team was accompanied by a BBC guy, but I don't think that this was the team which was "shockwaved".