That is way too much for a 2d game, my guess is that that game engine is just reserving that much but not actually using it. Unity loves doing stuff like that along with trying to hog CPU cores. Last I played around with Unity you could specify the amount of memory you wanted it to request from the system but in my experience most small developers don't know how to do that or just don't bother.
A lot of modern programs do the same thing, Chrome is notorious for trying to monopolize as much RAM as it can to the point of absurdity. A lot of video games do the same thing with GPU memory as well.
Normally memory is in given out it blocks per request but for you can set the engine to dump the entirety of the uncompressed game in to memory to speed up load times and avoid memory management altogether, my guess is that's what the dev did in this case; it's just a check box in the dev menu that says something along the lines of "speed up load times" or some such and most people click it without even thinking about what it is does.