I don't think it's that he doesn't believe; he's just being accurate to the point of pedantry about the relationship between BBC News and BBC Worldwide (or whatever entity will make the official announcement). Strictly speaking the BBC News story isn't official confirmation, though in practice I doubt they would have published if it weren't true.
If they're only inviting actors whose episodes have been recovered to the event, those names do suggest they've found even more than the three serials from the "MEW" (Marco, Enemy, Web) version of the rumor. 90 would still surprise me, but the claims of 20 or 30-odd episodes that were also circulating no longer seem incredible. And frankly, if it's that much, the claims that someone involved in the finding demanded the moon are easier to swallow as well; that much material is worth a lot to fans, which includes a lot of the people now making the series.