I constantly see Terry’s material being quoted out of context. To be more specific his conclusion was that the topic of a website does not matter. This is not the same as saying that an irrelevant backlink is useful for ranking because it isn’t.
A backlink must be relevant to see any significant ranking benefit. The website topic has no bearing on this, only the on-page SEO and particularly the anchor text and the words near the anchor.
I think you may have missed a nuance in what Angela has been telling folks. She has said that the website topic doesn’t matter, which makes since search engines do not rank websites they rank web pages. Angela gives very specific instructions that you must make your backlinks relevant by using relevant anchor text.
Irrelevant backlinks do little to nothing to help you rank for your targeted keyword. Don’t confuse website topic relevance with page relevance, they are not the same thing. For SEO website topic plays no role while on-page elements for your page as well as the pages that link to you are paramount.