This is one of those misunderstandings that cause no end of problems. Just because a paint is an “acrylic” does not mean that its carrier is water or that the paint is “water based.”
Tamiya acrylics are soluble in cellulose, aka volatile organic, thinners. That is, their thinners are either an alcohol (like X-20A) or a lacquer thinner (like Tamiya’s “yellow cap” lacquer thinner) or a combination (and there are some other common cellulose thinners that are also compatible with Tamiya paints). There is some confusion around this because both alcohol and lacquer thinners will take some amount of water into solution with them.
This leads many to believe that water is the intended thinner. “Hey, if water will mix into it, then water must be the correct thinner… Right?” No. Water is not the primary or even preferred thinner for Tamiya paint.
(And. for that matter, neither is glass cleaner which just happens to be mostly a combination of water, alcohol and ammonia - along with green and or blue dyes and some other detergents. The water and alcohol are discussed above, and ammonia just happens to be a solvent that is particularly well suited for organics. Which is why it "cuts’ grease so well in your kitchen. So, the ammonia assists the incorporation of the water into to the paint. However, ammonia is not a particularly good paint solvent since it has trouble evaporating quickly from the paint film. Consider… When the last time you bought a can of paint that had ammonia as the recommended thinner?)
Gunze’s paints are also in the same class of acrylics that are formulated to thin with cellulose thinners. This is why Gunze’s Mr. Leveling Thinner is considered by many to be a good (or even superior) alternative to Tamiya’s own proprietary thinners.
“Acrylic” used in any paint’s name or description simply refers to the method that the binders in that paint form long molecular chains when they cure to hold the paint to the surface, the pigments and to itself. Acrylic paints can be soluble in many kinds of thinners, not just water. There are water-based acrylics, petroleum-hydrocarbon based acrylics and cellulose based acrylics.