There is of course a spectrum of "indieness". You seem to be subscribing to the small indie theory, where the team is comprised of just a handful of people; the perpetual underdog.

On the other side are those who define indie as your level of freedom to do what you please with your product. In that case, even though they may be large and successful, being privately owned and without a 3rd party (ie. publisher) gives them the freedom to take their games in whatever direction they choose.

Vivendi was never a publisher for Activision, Blizzard or Activision Blizzard. It was merely their owner. Both companies as well as the merged version of them were always self-publishers. They were always independent of other publishers (sans Blizzard back in the early 90s, but that's besides the point).

The only thing they would ever lose being under Vivendi is their rainy day fund. They always had complete control.