Isolating an all-in raiser.

[Spidar]

B&M tourny. There's 50 players left and they're paying 36.

I'm SB with an avg stack of approx 20bb. I hold A7o.
BB has a stack of approx 60bb and is prone to defend. In addition, I've watched him twice call an all-in raise and check down a multi-way pot.
Short stack in CO pushes with little more than a BB.
With antes I'm getting about 2-1 with a call and do. I wiff the flop, check and then check down with BB.

BB and CO chop the pot. Afterwards CO whines that I should have protected his raise with a re-raise. I disagreed based on the above facts. Thoughts?