Exactly right. I watched a few of these types of videos yesterday, including one that attempts to explain how it works. The best I can put together from this is that the coke and the mentos have a chemical reaction that actually consumes the oxygen out of the water. As the oxygen drops down in the hole, the fish seek to come out where they can gulp air and get oxygen. These type of fish can breath water as well as air.
Yeah, this sounds plausible. I've also seen videos where these fish are actually digging holes to go down into as the water starts to subside. Many types of catfish do this. I'd be interested to see someone in the US try this in a flood zone where there are lots of catfish. You could probably get a cat fish trying this method.
Or at worst... you may end up with a snake coming after you!