The story is quite ubelievable but who am I to say it isn't true. To think that the stunt driver was knocked unconcious from the crash, remained so while the car filled with water as it sank 150ft to the bottom of the lake, then miraculously regained consciousness, escaped the car (including perhaps a racing harness/roll cage), and swam 150ft to the suface is remarkable.
By the way 150ft is not extremely deep for scuba diving, many tourist outfits will take you to that depth after about 15-20 dives (if you're certified). It obviously depends on the location.