He was going on the basis of the polls, which were almost all inaccurate.
I still think he is biased, but it is more subtle than screwing with the data as 270towin and the NYT do.
Nate Silver’s problem is like that of 99% of media/pundits. For simplicity, poll results show the midpoint of the result. If a poll says Clinton has 42% with a 3% MOE, it does not mean that 42% is more likely than any other point in the 6 point range. ALL POINTS IN THE RANGE ARE EQUALLY LIKELY TO BE THE “REAL” ANSWER.
Try redrawing the graph of poll results over time that Silver presents to show the rough sine wave. There would be so much overlap that your eye would tell you there’s very little pattern there.
You can’t use a yardstick as a micrometer. Polls are more like the former than the latter - even when honestly performed.