You're absolutely correct, that's not what "makes it so".
It's the facts that do that.
I know what the facts are. Trump was winning on election night. Then after midnight votes mysteriously started showing up for Biden.
Correct. That was the early and absentee votes being counted. A lot of states don't start counting them (by state law) until the polls are closed, or even the next day.
Because of Covid, there were a LOT more of them this year than usual, and because Trump had been beating the drum of how unreliable they were, a LOT more Democrats used them than Republicans.
They were counted later + there were a lot of them + they were mostly Democrats = Biden caught up. None of this was a surprise.