The download link on the GitHub is the uncompiled source code, and the download on others site is the compiled program(binary file). So you don't have to compile the program directly from a source.
Thanks a lot. However, I want to compile it myself for my PC and 2 nodes which are running on Devuan distro.
I was actually wondering myself because there is actually no source tarball on
https://bitcoin.org/en/download. There is a link there that brings me to the github repo. So I guess the only source tarball in on github.