Probably just afraid how investors in his fund would perceive his ability of managing their money after watching the video. If I viewed this video in the late 80s, I would doubt his abilities as he comes off as really reckless. Negative publicity is far worse than a losing year. In this game, reputation defines you.
What did Buffett say?... 5min to ruin a 20yr old reputation.
All in all, I find him to be a pretty decent guy and don't think there are any 'secrets' revealed in the video. If anything, it should serve as an inspiration looking as how he managed to turn a ~100mil fund into tens of billions as of present.
P.S. Perhaps he wanted to stop distribution because of the swimsuit model's picture hanging in his office.