That seems consistent with what the author is saying. Working inside of YouTube, he was in a position to see that the algorithms heavily promoted Brexit. Howev

That seems consistent with what the author is saying. Working inside of YouTube, he was in a position to see that the algorithms heavily promoted Brexit. However, for people not directly involved in YouTube's operations, this is not necessarily apparent — and is essentially impossible to check. His point is that the ultimate outcomes of this algorithmic selection has potentially massive societal repercussions, and therefore the citizenry deserves to know what is being selected for promotion.