The league has now officially chimed in, proclaiming Brown's action a punch.
Here's what a league spokesman wrote me:
"Duane Brown was fined $7,500 for unnecessary roughness. Specifically, on a pass play, he unnecessarily punched the opponent."
Yes, the play in question -- a strip sack by Session of Matt Schaub that resulted in a two-lateral return with the ball in Session's hands at the end -- is identified as a pass play, as Schaub intended to pass.
And thus ends our mini-punchgate.