A quick question in #srb2fun unearthed more people who were confused by that path, and while I have no idea why, the problems seem to revolve around the fountain-ish thing that blocks the view of the ledge with the rings on it, and the rock formation to the right of it that for some reason can be climbed on. Apparently some people thought that they were supposed to jump on those to get to the upper path. My suggestion is to remove those rocks (or at least make it impossible to jump on them like that) and delete the fountain or move it so that it doesn't block the view.
The whole setup doesn't make sense. First off, the actual, intended path has you traveling to the far end of the room, turn right along the wall, backtrack and ultimately cross over the place you just came from. Not only is this unintuitive because you need to go right in order to reach the path that leads to the left, but most players (myself included) will look for a way to get up there immediately, without having to first go forward and then double back. It doesn't help that there's an actual climbable strutcture that will get you up there, faster than the intended path.
Next, the detour to the right is easily missable because your focus is shifted to the left. Even if you didn't notice the overhanging path, the rising water flooding the corridor to the left will immediately grab your attention because it's a much greater contrast with the surrounding terrain. The right portion of the far wall, which you need to follow for the top path, should probably use a different texture as to more easily stand out and immediately convey that there's something different in each half of the room.
Then it doesn't help that even if you notice the detour, you come to a gaping hole in the path. It's right in the middle of an upwards ramp, and if your survival, let along gaming sensibilities are of anything worth, you'll immediately register this as "I'm not supposed to go through here". Add the fact that there's a Knuckles-only path in the room right after this one, and that the stage as a whole is architecturally pretty rough compared to the other levels in the game (except maybe CEZ1), and it's no wonder I never saw this as a viable, let alone intended and correct path for Sonic to take.
EDIT: Okay, granted, the map already uses two different textures on the far wall, but it ends up being ineffective because there's silver rock on the left and mossy tiles on the right, but right in front of where the right path starts there's also a random mass of silver rock in place of a proper staircase, which makes you miss the path split that's right in front of you. So get rid of those rocks in favor of a proper staircase, and also get rid of the rocks at the start which let you bypass the whole thing and we should be golden.