As you can see, above, what I said is that advertising from syndicates can (and are) on a category-by-category basis, and not on an advertisement-by-advertisement basis. I think you've missed all the distinctions I made between control over individual advertisements, and control over categories of advertisements. I hope this clears it up for you.
No, no one said that. What I said is that
subscribers to syndicated advertising cannot decide on an advertisement-by-advertisement basis whether they want a specific advertisement. Instead, going back to the first thing I wrote, agree to parameters for the advertising with the syndicate, i.e., categories, and perhaps even specific companies that should not be presented. (For example, I'm not sure they do, but the DIS might even specify a list of competitors to site sponsors, and direct the syndicate to not provide advertising from those specific companies.) However, again, the website doesn't get to review each advertisement before it is presented. Instead, then the syndicate decides what advertising will be presented, based on the parameters, and that's what gets presented.
And drawing this back to relevance... all indicates have been that the DIS has indeed indicated that political ads shouldn't be presented, and so what is most likely to have happened is that Google miscategorized the advertisement in question, and that's why it made it through to users.