The question is, how can heating it to a mere 100 to 110 or so during extraction produce this bad burned taste?
Answer: We grind coffee very finely, making it far, far, far, far more susceptible to temperature changes. Water conducts temperature far greater than air as well. A bean in a roaster takes minutes to reach a high temperature, but in a portafilter it takes seconds (or less), AND it's finely ground. Burning happens easily, and how it gets in the cup is no surprise, although interesting to theorize about.