We were there for the Shootout of '09 (and, for that matter, of '08 and of '10, and probably will be for '11, etc.)
Curt said that since he was on a record return run he was anxious to get the car moving so gave it a bit extra throttle. The Duramax is turbo-ed, of course, and the boost came on quite suddenly - and that's why he spun. He was all but laughing when he got back to the start for another try. One reason he was in a hurry was the one-hour clock was running and the team had very little time to spare. As I remember he did qualify for a record there -- I think.
As for the canopy opening, as far as I can remember the latch opened because of the side winds (so to speak) when he was going around. The breeze pushed the latching device stuff far enough sideways that bingo -- it was opened. But it was, indeed, latched before he got pushed off. Neither Lynn nor Mike Cook would have missed checking that before starting.