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He said that he sucked up some water. CAI's that are near the ground (like the original TRD) can suck water into the engine if you drive through enough water. Since water doesn't compress, when the piston comes up on a cylinder full of water things break (hydrolock). AEM makes a bypass valve to go inline on a cai in case the end is submerged. They have a video of a car where they stick the end of the cai in a bucket of water to show that the bypass works and it doesn't suck water.

 

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I figured there had to be an answer like this, thanks very cool to know

is this kind of damage pretty rare? even for people with cais

It was a big topic of discussion here a few years ago shortly after I joined the forum. I believe one member (don't remember his name, but he had an RS 6 like me) had it happen to him.

You have to have a cai that opens low to the ground and you have to drive through deep enough water for it to be submerged (or nearly so I would think). I doubt that combination happens all that often. When it does though I would expect it to hydrolock every time. I am curious whether that would be covered under comprehensive insurance (like when mice chewed up my wiring harness).