The vote spikes are simple - early voting ballots getting reported [1]. Biden encouraged his supporters to vote early. Trump did the opposite. Accordingly, the early/absentee votes are ~90% for Biden. Due to the way they get counted they come in larger lumps than day-of vote counting. As far as I can tell the rest of the post is statistical gish-gallop with some graphs and equations to make it all look more convincing.

I also want to say that the sources of reported votes isn't a mystery, and the author could easily have found out that they were early votes if they had wanted to. Either they didn't check, or didn't want to inform people of those very relevant facts.

[1]: https://www.reuters.com/article/uk-factcheck-wi-pa-mi-vote-s...