So it was a rumoured tweet. That was announced as a rumour.
Best to wait for official announcements.
"From the beginning, there have been reasons to doubt that the rumor will hold up. In particular, LIGO researchers purposefully inject false signals in to their data to test the sensitivity of their analysis techniques and to keep people honest. Only a handful of people know when the fake signals are injected, and they reveal that information only at the very end of the process, after researchers have gone through all the checks to validate a signal. In fact, LIGO researchers thought they had discovered a signal on 16 September 2010, just before they shut down for the rebuild. But it turned out to be an injected signal, which the researchers found out only as they were about to submit for publication a paper claiming a discovery. That procedure would seem to render it impossible for LIGO researchers to know for 3 months whether they had a real signal or not."