After doing some googling it's apparently from a Twitch stream from one of the writers. The stream itself seems to have been lost since Twitch didn't save it, but for those interested there's a summary on the various highlights which can be found here:
https://www.reddit.com/r/BaldursGate3/comments/jd1qsq/highlights_from_kevin_vanords_stream/

The quote about companions is
Quote
*They plan to have eight companions, possibly more, and potentially including companions that won't be origin characters

*There will be more companions than DoS2 but possibly less than BG2. Part of the "less than BG2" bit is because they want all the companions to have fleshed out stories