Is this a light effect, or heterochromia?

Both eyes: http://imgur.com/ll8aidH

It could be sectoral heterochromia where part of the iris is a different colour.

I think the simple answer is – - >

A )The lens on the phone is offset (not centered on phone)

B) the lighting is from the back

Therefore the left eye is partially covered by the phone.

Basic photography, “Don’t get shadow of photographer in shot!”
Your phone is black right !
Try same shot with diffused light or light overhead.

I made some more images under different angles. They look the same.
I guess you were right, it was a shadow.

I took a couple of classes for photography. Got marked down on an other wise great shot, my shadow was in a corner of the shot. Should have cropped it out.