What does the II above the numbers in the strumming section mean?
The pattern diagram appears to separate the count into four separations, seeing how the up arrow is coming in on the second half of the &.
Another way to count it would be the syllables One - E - And - Uh, where on count is broken into four beats, or one quarter note separated into sixteenths.
The strumming would be coming in on the And - Uh, or back two beats of each count, or the last two sixteenths of each count, down strum on the "And", up strum on the "uh".
e + uh e + uh e + uh e + uh 1 . . . 2 . . . 3 . . . 4 . . . ↓ ↑ ↓ ↑ ↓ ↑ ↓ ↑
The two lines then are representing the two beats of the first half of the count.
Edit: looking at it again, I suspect the two lines are the PAUSE symbol...