Funny seeing so many people trying to convince themselves Bo pinned himself (not here so much but seeing it in lots of comments on Flo and elsewhere). Watching the replay it's clear that at one point his shoulders are flat, but for far less than a second, and his being there at all is not by Brooks' doing.
My interpretation of the rule has always been that, though the offensive wrestler can effectively pin himself, there needs to be some causal connection between the defensive wrestler and the pin. Here's the rule:
Any part of both shoulders or part of both scapulae (For pinning area, see Illustration No. 2.) of either wrestler held in contact with the mat for one second constitutes a fall. The one-second count (one-thousand-one) shall be a silent count by the referee and shall start only after the referee is in position to observe that a fall is imminent, after which the shoulders or scapulae area must be held in continuous contact with the mat for one second before a fall is awarded.
Since the rules don't define what it means by "held," I'm willing to interpret "held" broadly enough based on past practice to mean that very little need be done by the defensive wrestler to cause the offensive wrestler to "pin himself." But not so broad as to be deprived of all meaning. I interpret "held" to mean simply that the defensive wrestler had the intent to pin the offensive wrestler, usually indicated by some positional awareness, like, say, backing into the offensive wrestler in a crab ride.
Brooks's only intent there was to look less ridiculous as soon as possible, he had no awareness of where Bo's shoulders were. But again, to the extent Bo was ever flat it was for far less than even a half second.