I've always hated PFF's OL grading. They have JR Sweezy as the lowest rated starter on our line. Granted, he did make a big mistake that led to a sack in the last game, but generally he's been fairly good in protection since the start of last year and he's a monster in the run game.
As far as our protection as a whole, Washington blitzed the crap out of Seattle and only got 2 sacks for it (the 3rd sack was intentional on Wilson's part to keep the clock running at the very end of the game).
When a QB gets sacked on a blitz, you can't really put that on the OL anyway. A QB has a lot of responsibility for beating the blitz.
According to the chart, only about 20% of Seattle's value from the last game came from our ballcarriers when running the ball, compared to 40% for run blocking. That seems to be a bit of a stretch in a game where a QB scrambled for 122 yards, which obviously has zilch to do with run blocking.
Anyway, their scoring system is kind of a mess, though it does occasionally have its moments.