I've bought the taunt earlier today and I've noticed two flaws with the animation:
1. the animation where the pyro pushes the key at times doesn't match with the note it's playing; sometimes you would see pyro hitting a key but no notes were played. It simply feels like the animation is longer than the audio.
2. the looping is rather imperfect; instead of the pyro keeps playing non-stop, sometimes his hands just stop playing and returns to the default position for a split second before reaching for the piano to start playing again.

This [drive.google.com] video might just explain it better.