No, we cannot say Bob made a mistake. The best we can do is say we don't know if he made a mistake - he was guided by his EWT. If the SP falls to $120 tomorrow, he will have made the right decision. EWT predicts the SP will fall to $120, but the problem is, it cannot tell us when it will happen.
I once told someone that the earth is round. He said, how do u know...? I said I walked, and walked, and walked further still, and I never fell off the end, so the earth must be round. Not so, he said - the earth is flat, and the reason why u didn't fall off the end is because u didn't walk far enough.
This is EWT in a nutshell. If the SP rises to $1000 tomorrow, we cannot say EWT is wrong in its prediction that it will fall to $120, because the response will be "you haven't waited long enough". Also, when the EWT theorists discover that there's something wrong with their waves, they simply re-draw them based upon an entirely different set of observations and assumptions. In other words, EWT can never be proven wrong. This is both the strength (if you can call it a strength), and weakness of EWT. It's sloppy thinking, it's lazy logic, it's "voodoo" at its best.
(20min delay)