Sort of right, sort of not. Clutch fluid is the same as brake fluid. It is a largely incompressible hydraulic fluid. Water is also not very compressible and because of that, it's also a theoretically effective fluid to use in a hydraulic system like a brake or clutch line. In the current context, an important difference between the two is that water tends to give rise to corrosion and brake fluid does not. (Viscosity and lubricating properties are probably also important differences, but not necessarily relevant to this conversation).
A couple of other important differences: brake fluid is an awesomely effective paint remover (meaning: don't spill it on your paint, or your electrical wiring, etc. It works pretty fast and you should always have some rags close at hand if you are working with brake/clutch fluid). Another important difference is that brake fluid is hygroscopic: it sucks moisture out of humid air perhaps even more effectively than a salt shaker will clog up on a humid summer day. If you pull the cover off the clutch or brake fluid reservoir to check the fluid level, you probably introduced some small amount of moisture into the fluid just by doing that. In theory, if you never remove the cover, then it seems like there shouldn't be any opportunities for moisture to enter the fluid until the car has aged significantly and the various rubber seals in the cover and actuating cylinders start to break down.
Which leaves me wondering why Kia is suggesting that the clutch fluid should be replaced every 18 months or 22,500 miles. In days gone by (when cars in the rust belt only lived about 100,000 miles), no one ever replaced brake or clutch fluid, and usually the car failed catastrophically in some other way (frame, engine) before the hydraulic systems failed, although it's probably fair to say that at 100,000 miles, the hydraulic systems were showing their age due to the onset of corrosion causing things to not move as freely as they did when new. Now that cars can live to a lot higher mileage/years, it seems to me that it does make sense to replace the hydraulic fluid in both the brake line and the clutch line at some point, but I'm questioning if 18 months/22,500 miles might be overkill. If I recall correctly, Kia doesn't say anything about replacing the brake fluid (which is chemically the same fluid, but there's quite a bit more of it in the reservoir and brake lines and cylinders). I'm thinking that anyone who wants to drive their car for a really long time and not worry about leaking brake lines or cylinders would do well to replace the brake fluid around 80,000 miles or perhaps 6 years, which ever comes first. It seems to me like the same should hold true for the clutch line, but I'm not an expert, and I have no idea why Kia thinks it needs to be changed more frequently than that.
Perhaps some of this guidance is being driven by Kia's prior experience with issues that showed up in other models that they sold a long time ago.
2018 Niro PHEV Gravity Blue