It looks like the "super heavy chops" referred to here have mostly corkscrew spin. Ayuka lets the ball drop considerably, then makes the stroke sideways under the ball. The stroke impact is hidden from the opponent and easily mistaken for underspin. Opening the racket to return underspin will allow the corkscrew spin to "bite", and the ball goes in an unexpected direction. The spin seems to be "too heavy to handle" but most likely there is less spin than a regular underspin chop would have. The effect is so prominent because the receiver expects a different spin and does not compensate for corkscrew spin.
In most references to corkscrew spin for table tennis, you will see that it is more or less "exclusively on high toss serves". Ayuka lets the ball drop to emulate the effect of high toss (vertical speed), which enables her to make those returns. It is not very difficult to do it. The challenge is in keeping it low enough that the opponent won't smash it. A flat hit such as a smash will largely avoid the effect of corkscrew spin.
See this:
http://masatenisi.org/english/spin.htm