It is definitely good enough to sample the signals. But why use an inaccurate title? Wiring something into a soundcard doesn't make it a microphone.
The title is a word play summarizing the fact that the author used such an amp to record biological signals. In context, it doesn't means or even imply that he uses a microphone.
Edit: word play, not pun; Edit2: +s; 3: better still.
Editing, anyway.
edit: that part meant jokingly (please). Although https://en.wikipedia.org/wiki/Old_English_grammar#Pronouns is far more interesting.