As far as i know, he's just showcasing his progress as personal skin and have no plans on releasing it.
I agree that a mention or ask is a better approach. But not everything can be traced back, unless it's very specific..
We all use "some" things from other skins in one way or another without mention.. some of those things may be removed later on or changed to suit the skin in a better way.. i've done it, you've done it.