These accidents seem to happen to the freaks many times before the lesson is learned.OK..before I respond I want to say I am truly sorry for the injury you sustained. Believe me I have shot my self similarly with nail guns. In fact I shot a nail through a facia board, through my finger and into the rafter tail while standing on the top of a ladder and had to pull the nail out with the claw of my hammer to get down. It hurt...twice.
With that out of the way...the point of my question "how is this a freak accident" was to point out that you, like me, pointed a nailgun at your hand, pushed it to the board to release the safety and pulled the trigger. If you repeat all the steps exactly the same way...it will result in the same effect.
In the interest of learning instead of calling it a "freak accident" perhaps "really dumb mishap" or "jackass moment" is more appropriate.
The last time I shot myself with a framegun and 3" frame nail I was nailing a plate to the studs. I was in a hurry as usual. I shot a nail and the gun bumped back and reset again but on the edge of the plate so the nail missed the plate and shot the nail about 6-8 inches and into my left hand holding the stud. It went in about 2 of the 3 inch length. I thought it went through my knuckle of my index finger. I had to pull it out with some pliers. The doctor said I should have left it in there so they would know exactly where it went. He said It obviously missed the bones but had it not it would have been a much worse injury probably requiring surgery.
Glad you feel better. Bet you try to avoid that "freak" from now on. Pain is a good teacher.