has nothing to do with open source

    long time ago

Sourceforge is almost 30 years old. GitHub almost 20.

How long does something have to be done a certain way for it to be "to do with"?

I would say we're now two generations deep of software engineers who came up with open source software commonly being mediated through public issue trackers.

That isn't to say it needs to stay that way, just that I think a lot of people do in fact associate public project tracking with open source software.