I wouldn't say they 'shouldn't' have advertised the stream. The event was still interesting, and I had a fun time.
We have to remember that Boostr is a French Company. Now I haven't been to the French section of the forums since that one (curious) time long ago, but I would presume the majority of players are also French (also corroborated by the live-stream chat). It then makes sence for French to be the main language.
We should presume most 'live' media would be in French, not English (though a Spanish-Language event would be interesting...). In the future, they should merely announce if a stream will be available in English, not 'don't announce it at all'. Next time, I'll try to get my Québécois friend to watch, and see how well he will understand it.
As for the Teaser, it was good. I'm personally confused about the 'theme' of the new clan, and how it will fit into the current 'lore' (Does UR have a standard set of Lore? I feel like staff makes it up as they go...). But that will come in time. I'm also not one to ride the hype-train from the starting station... I liked the addition of the timeline at the end. I think that got me the most excited.