I'd say it's more natural than suspect. We all extrapolate, it's a survival skill that allows us to make certain predictions. I guess doing it publicly is human nature, too. As for the chain brake, I never said what happened to my Ryobi happened to the Stihl in question, and certainly I pass no judgment on Stihls, I've been mostly happy with mine. But just because something is unlikely doesn't mean it can be dismissed. As Carl Sagan said, given an infinite universe, anything not specifically prohibited by the laws of nature is mandatory. We don't have an infinite number of users here, but it's a fairly large sample, and since most people (or their friends, increasing the sample size) seem to post mainly their gripes it's just a matter of time before everything that can possibly go wrong with a saw, does.
My first thought reading this thread was that Tom was right, the guy set the brake by accident, kept mashing the trigger, smoke, done. Happens every day, and nobody wants to admit to it. But John said no, his friend is a stand up guy, that's not the way it happened. What he said happened, that the saw SLOWED DOWN AS he was cutting, then stopped, would be far more improbable if the brake were accidentally set than either the possibility that the brake was making partial contact in the off position or that he revising his personal history in order to avoid admitting his mistake. Ergo, either the brake band was making partial contact or history is being revised. We may have our suspicions, but the door is open for further evidence to decide the issue. In any case, I think it's more interesting to think about ways an unlikely event could happen than simply to join in berating the owner.
Jack