If it was a real wormhole type effect you would expect to see the other side when the gate opened rather than the cool water effect, and have bi directional travel rather than the single direction that appears to exist.
I've always wondered about the entire "single directional" thing. I mean, if it's unidirectional, how come they can send the probe robot through and expect to get anything useful to come back, and why doesn't the room immediately start depressurizing the moment the gate is opened? If it's unidirectional, it would function as Maxwell's Demon, and result in all the air in the room blowing out. A gate opened out in the open would start sucking off the planet's atmosphere, and a gate opened at the bottom of the ocean would drain the ocean.
Both of these points were addressed more than once. The Stargates pass radio
both ways; it's in the design, probably because the designers wanted to be able to communicate through the Stargates. As for atmosphere, the Stargates are designed specifically not to allow more than a tiny amount of air exchange between gates; again, this is by design, since planets don't have the same atmospheric pressure. Also, Stargates might be in vacuum or under water. The simple answer is that they were designed that way by the original Builders, and even Dr. Carter admitted she didn't understand everything
about how the gates worked.
The main reason air doesn't leak or blast through the Stargates is "because." Because they were designed by highly-advanced people who were smart enough to design them NOT to do stupid things. You might as well ask "why don't people who walk through the Stargate take off in the direction of their last linear and angular momentum?" Because the builders weren't idiots, and the Stargates automatically translate one's linear and angular momentum so that you have precisely the same momenta in the new reference frame. Now "why do bullets and arrows travel through with lethal effect?" We learned that when we discovered that the Ancients built small spacecraft which can travel through the Stargate. There are good reasons one would want to be able to fly out of a Stargate at high velocity, although if one were to fly a Puddle-jumper through the Stargate at rifle velocities ( Mach 3-4), the compression wave would probably kill everyone near the 'Gate. That's not a bad thing if you know there may be hostiles on the other side. The same holds true for Staff blasts. "Because the designers built it that way" is really a very good explanation. If you want a better answer, Ascend and ask an Ancient.