Yes, it's definitely official. Vocus stays in for the next quarter. Check the announcements for LYC (for example). They have published the official release from S&P.
And yes, a bit of buy-back this morning but without volume.
Vocus is staying in the ASX100 list because it satisfies the criteria, not because somebody decided "hey, it would be nice to have Vocus in the index".
VOC Price at posting:
$2.94 Sentiment: Sell Disclosure: Not Held