this should not happen and your contractor is most likely at fault. This cost and repair should not be your burden.
Do as Jay J states, get pictures, get names, get documentation, get facts, get assistance, I mean legal.
These vents are seen on many homes. Unless you had wind sheer with rain, this should not have happened.
You need to see if this is where the water actually came in. Maybe go in the attic and see if you can see some dark running water stains. remember, the leak actually hits the ceiling way down from water entry.
you might have had a bad tar paper job, a nail exposed outside the tabs, or bad flashing, or bad cuts around stacks. There are so many OTHER areas where this could have occured.
Let this contractor know that you are upset, and that you want satisfaction. Don't let him blame the ridge vent system. It is not at fault, if so many other people would complain about this water leak.
YOu are close to getting screwed and don't let it happen.
Hang in there and stop being so easy with this guy.
Damn, I get wound up when a person gets the shaft from a contractor.