1. Google did not build Android from scratch, Google bought the company which created Android, and built it to a releasable platform from there.
2. Inferno has nothing to do with Google, the only (remote) link is that Inferno is that Ken Thompson worked on its predecessor (Plan9). I'm not even sure Thompson worked on Inferno itself.
3. I've never seen any claim that Google uses Inferno anywhere.
So a better question would be: what makes you bring up Inferno in a place where it has no reason whatsoever to be?
Code reuse at Google is huge.
So what were their reasons for not choosing it?
Apologies if this has been asked and answered.