You can see the beating here. It's a E flat and a G, which are related harmonically, and when I tune a piano, I at least try to get these intervals to not beat. But you can see clearly here that it's intentionally like this since this is not even a real piano - it's tuned this way for some reason.
For those who don't know what they're looking at, the spectral display shows, by the brightness of the yellow bands, the energy of each frequency going up the chart (Y axis). For each line, it's the energy of one frequency. When you see disjointed lines, that's beating, or the twanginess you hear when something is nearly in tune, but not perfectly.
Guess it could be the temperament. I was never good at understanding the effect of different temperaments, but I suppose this is probably one of them.
