If you are trying to install stable openHAB that is the wrong link. That is a link to the temporary site will what will be the next version,. openHAB 3.
The SmartThings configuration documentation is here.
That looks like an official source repo link but jar files to install are never stored there. The source code was recently reorganized to archive OH2 addons in preparation for openHAB 3.
It’s not about the jar. In smartthings you need to install 2 groovy scripts to make the binding work with openHAB. The url points to those 2 scripts. Theoretically it might a different script for different versions of the binding and therefor it’s tricky to point in the documentation to an unspecified version on GitHub…
It is unfortunate that one has to resort to copying and pasting to get the code into the Smartthings hub. Right now there is no other way. I recently bought Inovelli and Zooz switches. They both required the same process to get their custom device handlers installed.