No, no, some open source licenses require you to publish internal changes. Eg some are explicitly written that you have to publish even when you 'only' use the changes on your own servers. (Not having to publish that was seen as a loophole for cloud companies to exploit.)

Those clauses exclude those licenses from some very important definitions of free/open-source software. For example they would fail the Desert Island Test for the Debian Free Software Guidelines.

The point he's making is that who is going to actually enforce that? If I take something that has that license and make changes to it, who is going to know? That's the underlying premise here.