The terms of use is basically a clickwrap https://en.wikipedia.org/wiki/Clickwrap agreement, right? When you make a contribution, you see "by clicking you accept blah blah blah" somewhere, once you click knowing that, you made a sort of contract from a legal point of view. So the terms of use only applies to you if you do actually see that piece of text, which does not seem to be present on mediawiki.org, nor on gerrit.wikimedia.org, and obviously not in the git interface when you are pushing a patch.
I agree with this reading, but I also think people like Bartosz will be legitimately confused.