I did a bit of testing. Its tricky, difficult to perform, and unlikely to be done in a real match. This could be game changing for tournaments, or with hours of practice knowing exactly where to jump it can be more conventional. I still don't know exactly where to jump from, but I have a general idea of where to aim it. Aim at the right wall on the corner, then mash jump and go left as soon as you hit the wall. Jumping is key, because it pushes you up faster than the wall can detect your placement, and it puts you enough distance away from the beam for the hitbox not to knock you back. I usually end up just falling off the wall, but a few times I made it up. One time with ninja squid, and the rest with max swim speed. Ninja squid is even more picky, but not impossible.
Its just a programming oversight, not really clipping. The bar or the corner isn't wide enough to cover the entire area you can swim up. I think its more like the Camp Triggerfish bridge jump than anything else; just a creative way around a wall that the programmers didn't think to check in such a specific way.