I was wondering the same thing, but I think that a part of the project is exploring the concept that perhaps one day prostheses will no longer just bring those who need them up to parity with the rest of the population, but will instead extend them past the natural capabilities of a human. Technologically the creators could've recorded these sounds with an iPhone, but the message would've been different.

They're exploring the same space as Neil Harbisson's Eyeborg project [0] and John Scalzi's book Lock In [1].

[0] http://mashable.com/2013/06/01/eyeborg/

[1] http://www.avclub.com/review/john-scalzis-lock-crams-big-ide...