Nope, public repos have license, often open source licenses that state that you can freely use the code, or change it , but only if the resulting product will also be opensource.

Other licenses such as the MIT license require that you name the original creator.

You don't need to accept that license to download and read the code.

But no license (that I'm aware of) says "You are allowed to read this source code, but you may not produce work as a result of learning from it"; for a start, that would clearly be impractical to enforce.