The spirit should be more like 'This repo is a fork of'; The language you chose suggests that his project was derived from yours. Also, I think you need to do slightly different things to comply with the license. It says:

"You must give appropriate credit, provide a link to the license, and indicate if changes were made. You may do so in any reasonable manner, but not in any way that suggests the licensor endorses you or your use."

http://creativecommons.org/licenses/by-nc/4.0/