talking legalese always begs the question. If you follow the timeline you'll avoid the circular argument. The huge increase in trading took place and the BOM upgrade was done, after the RUMOR. The company, Ariad, could have quashed the rumor immediately as they have done in the past, but chose instead to remain "silent" as you say, letting the enourmous trading to take place.
There must be a very good reason, and it is not the one you are pointing out.
It is common sense to assume that any of the parties involved would say something if the "rumor" was absolutely untrue, especially, Ariad, who has the biggest investor exposure to the rumor. NASDAQ rules for legal reasons require companies to explain and/or deny any rumors that can lead to investors' litigation. Therefore, the fact that we haven't heard a thing by now, days after the rumor came out, it only points to the conclusion that all or parts of the rumor are indeed true. And the parties involved cannot disclose anything at the time being due to the sensitivity of the negotiations.