Why do we think so? Well, the original Galaxy S is the I9000, the Galaxy S II is the I9100, and the Galaxy S III is the I9300. Although we can't be completely certain, it makes sense for the I9400 to be the Galaxy S IV. Of course, if you look closely at the screenshot, you'll notice that the device is listed with some pretty mediocre specs (for a GS IV), like a screen with WVGA resolution, and 1.2GHz CPU with Mali-400 MP GPU. This shouldn't disappoint you, as it doesn't mean that this isn't really the GS IV. In fact, when the GS III first leaked, it, too, was listed with such weak specs, but naturally, it later turned out to be the monster everyone expected it to be.
It may be a bit early, considering that Samsung isn't likely to announce the next Galaxy S until the middle of next year, but it's always fun when we start hearing rumors and speculation about an upcoming handset. Let's hope that this benchmark entry will be the first of many leaks about the Galaxy S IV!