Icahn wouldn't be above sending a tweet like that to raise the price before unloading shares. His goal is to maximize his return, not that of his twitter followers.
NEW YORK, Aug. 12, 2013 (GLOBE NEWSWIRE) [..]
Our Chairman, Carl C. Icahn, intends to
use Twitter from time to time to communicate
with the public about our company and other
issues.
[..]
It is possible that the information that Mr.
Icahn posts on Twitter [..] could be deemed
to be material information.
Source: http://www.ielp.com/releasedetail.cfm?ReleaseID=784592If anything, Icahn's tweet signals that he is no longer purchasing AAPL in quantity. Now he wants the market to "catch up" to his value appraisal so he can realize a gain.
http://www.buzzfeed.com/mariahsummers/if-you-want-to-be-a-tw...