A look at how some subreddits overlap:
https://fivethirtyeight.com/features/dissecting-trumps-most-rabid-online-following/
Fits best in here, I think.
This was an ignorant article and the writer is getting currently lectured in some of those subreddits as we speak. I give him props for stepping into the threads and admitting he wrote the article. I'll give him more props if he listens to the people and realizes his mistakes.
What he did was take a presumption, then create a formula, and he changed the variables of that formula until he got the results that best let him write his presumption. The overlap between t_d and /r/Conservative isn't clickbait enough, so keep switching around what you subtract from or add to the maingroup until you get a spicy headline. On top of that, he erroneously labeled some subreddits as hate reddits out of his own ignorance.
To go a bit further:
The fact that commenting in a subreddit doesn't mean you support that subreddit doesn't seem to even be taken into question. Consider the overlap between t_d and r/games resulting in TotalBiscuit's subreddit. TB is about as anti-Trump as you can get, and he has gone on rants about Trump, which has resulted in some of his fans getting angry at being labeled racists by him. This then lead to a further discussion between himself and his users on why they vote the way they do. There is discussion between Trump people and TB people without agreement. The overlap is a result of a disagreement rather than agreement, and the conversations that followed. However, if you read this shite article then you'd think TB was a Trumpee.
Data doesn't lie about the data it produces, but the people doing the data lie about what the production means. Analytics are not a substitute for poor observational analysis, and those that lack in that mental specialization who overcompensate for it with heaps of data are doing harm.
Also, my general rule is no to take seriously any article about the internet that doesn't first invoke and understand the mechanics of or the post-irony nature of the net. This nonsense from 538 is exactly why I have the rule. The overlap between donald and 4chan speaks to something entirely different but very relative to any racist overlap. If you don't bother to understand or explain this then you're being dishonest. You're lying via omission and prove t_d right in calling your site fake news.