It does seem odd. Assuming the two animations have different times/frames at which the hurtbox would appear, this is going to lead to either inconsistent animation or an attack with a variable/random speed. Either way, it's bad, since players then have to learn two separate timings for one attack, and even then cannot predict which will be used at any given time.
I had noticed too, i am assumed that the fast one was supposed to play if you didn't hit anything and the slow one played if you hit something, but now its obvious that its just random. Hopefully it gets addressed, because if they put the effort into adding the animations then it must have been done for a reason.
Comments
I honestly didn't notice, and it hasn't affected my ability to use it in the slightest.