I think Cy sees this as very black and white (either Ainge is an honest, upfront guy or he's a dishonest, scheming scumbag), which is no wonder why he doesn't seem to appreciate that even those at the highest level still have all the human characteristics as the rest of us. Interestingly, as already mentioned, he doesn't seem to have an issue with believing Cleveland is being dishonest. Also, with regard to the whole medical evaluation thing, it's also not black and white. You can't just plug in all the variables and expect some kind of science to compute you the same answer every time. Ainge could have very well known his health is a bigger issue than being let on but figured he could roll the dice on an independent evaluation (as he probably had many conflicting medical evals in his own camp anyway). This was kind of the crux of the whole Bosh issue (assuming that there's a universal standard agreement in medical evaluations), and an issue I'll eventually readdress.
Cleveland certainly could be blowing steam, but would they sacrifice what they thought was a good deal (if they assumed IT was healthy enough) to hold out for a draft pick? Seems awfully risky and shortsighted. However, if they felt iffy about the deal to begin with then it's possible this pushes them over the edge. But, if it's too late for Boston to back out (based on rules or what have you), then maybe they really are messing with him.