When you install python for windows, there is an option to include it in the path. For python 2 this is not the default. It adds the python installation folder and script folder to the Windows path. When starting the GIT Bash command prompt, it have included it in the linux PATH variable.
If you start the python installation again, you should select the option Change python and in the next step you can "Add python.exe to Path". Next time you open GIT Bash, the path is correct.