It is very typical of the government to try and pass unpopular bills while the public is distracted by something else. I find it rather disgusting that the government is willing to use a bombing to their advantage to pass some legislation that is not necessary. But hey, it's the government after all.
Although the house may not have intentionally waited specifically for the Boston manhunt, they definitely took advantage of the fact that the nation and the media was distracted by the bomber manhunt. The timing lines up perfectly, vote and pass CISPA while everyone's eyes are glued to terrorists on the run on the television. They know media outlets aren't going to take precious airtime away from the number 1 news story to discuss current legislation, and the hopped on the opportunity.
The timing is bad, but there is no evidence that the two are linked. The bill has been known about for months, and to assume that the Boston bombing was caused or used as distraction is a jump in logic, ahead of the evidence. Just because my foot tingled before it rained, doesn't mean the two are completely linked. I think people connecting the two events are grasping at straws, without the evidence other than the two events to corroborate themselves.
It was unfortunate timing that CISPA was passed shortly after the US stopped paying attention and began watching the Boston manhunt, that's all. This bill has been in the house for months and as it hasn't received as much attention as SOPA, it was passed - it was flying just under the radar to the general public.