git.exe is common for any git based applications like GitHub, Bitbucket etc. Some times it is possible that you have already installed another git based application so git.exe will be present in the bin folder of that application.
For example if you installed bitbucket before github in your PC, you will find git.exe in C:\Users\{username}\AppData\Local\Atlassian\SourceTree\git_local\bin
instead of C:\Users\{username}\AppData\Local\GitHub\PortableGit.....\bin
.