"as well as being in the right place at the right time..."
Just going by your statement that he "made a lot of REALLY bad business decisions...in the first 25 or so years," it seems like he was at a lot of different places at a lot of different times. This very much increases the probability of eventually being at one of the right places at one of the right times.
To Clarify - in his book he makes it seem like if he never signed Miked Oldfeld (Tubular Bells), then the company would have gone bust in its first few years, and that 25 year period would never have happened.
Hence, it was being in the right place at the right time once which allowed those future bad decisions to be made.
Just going by your statement that he "made a lot of REALLY bad business decisions...in the first 25 or so years," it seems like he was at a lot of different places at a lot of different times. This very much increases the probability of eventually being at one of the right places at one of the right times.