Your coin flip analogy is spot on. But instead of a 1 in 2 probability, Trump had a 1 in 10 probability of winning. We knew this probability precisely because of polling data (and historical error).
This wasn’t some rare weird outcome. This was probably a standard deviation or so closer to Trump in a forecast. Perfectly normal thing to happen.
Sure, the model had value precisely because it said that even if Trump did better than the polls suggested, he would likely still lose due to the paths of victory Biden had. That said, the polls have shown, in many cases, poor predictive behavior of actual votes, and as such, we should not just brush this off by quoting the distribution of outcomes.
This wasn’t some rare weird outcome. This was probably a standard deviation or so closer to Trump in a forecast. Perfectly normal thing to happen.