This tweet is incredibly dumb.
Firstly you can't just look at one candidate's support in isolation, because usually there are significant numbers of third-party and undecided voters. Actually these were really high in 2016, so it's pretty common for both the main parties to beat their 2016 polls, but the Democrats usually beat theirs by much more.
Secondly the 2016 election was on the 8th, not the 3rd, so it makes no sense to have a common x axis with the calendar date - "number of days from election" would be more appropriate. When you're a long way out from the election, 5 days isn't very much, but the difference between being 7 days out and 12 days out is pretty big, especially bearing in mind the high rates of early voting this time.
Thirdly there is no reason to believe that the swing state polls will overstate Biden's support the same amount that they overstated Hillary's support. Historically the errors have jumped around - it's possible that they will be out even further in the same direction, but it's also possible they will be out in the opposite direction from last time. So it's hard to draw any conclusions from comparing the 2020 polls to the 2016 polls.
Yeah, I got sucked into that for a while, before gradually noticing that a lot of the stuff they were laughing at ("headmates", "transethnic" people, etc.) seemed to be limited to a few extremely obscure Tumblr accounts instead of being widespread phenomena. A lot of communities that are based around dunking on people fall into the trap of focusing almost all of their attention on a tiny number of trolls and people with obscure personality disorders, but TIA fell for it really hard.
Also finally getting a little bit of exposure to sociology and philosophy made me a lot more open-minded about political and cultural movements. Even if there were a massive, influential community of Otherkin, it's hard to argue that it's any weirder or more threatening than, say, Christianity or car enthusiasts.