Nice field repair.
We did some research several years back to determine why rear tires were punctured more often than front; at that time it was a 9:1 ratio. I was a member of the American Society of Fleet Managers at the time (and an Iron Butt Association motorcyclist).
We determined that the front tire would grab and upright the offending piece of debris and luck would take over from there. If you were going the appropriate speed for that particular piece of debris to re-engage it while it was at the correct attack vector for your rear tire, you got your puncture.
Not much to be done about it; just an interesting bit of tire trivia.