If I understand correctly what he meant by “a probability problem”, your prior that the coin is biased is 0.
I meant "The 'correct' answer when you're taking a probability class or are taking part in a study examining gambling fallacies and don't want to be counted as one of the people who 'clearly' doesn't understand probabilities."
That said, I actually had a decent probability and statistics coursework instructor who would have marked "~100%" correct if a decent explanation were provided for the answer. (I answered problems that way all the time, although I don't think that exact question turned up in any tests even though it did turn up in the probability textbook.)
The chapter on judgment under uncertainty in the (excellent) new Oxford Handbook of Cognitive Psychology has a handy little section on recent critiques of the "heuristics and biases" tradition. It also discusses problems with the somewhat-competing "fast and frugal heuristics" school of thought, but for now let me just quote the section on heuristics and biases (pp. 608-609):
My thanks to MIRI intern Stephen Barnes for transcribing this text.