Series 11 story arc

Why is everyone thinking that the series arc Chris Chibnall said he is going to do will be one 12 part story. I am really confused why people think this. I have read the article and it just mentions a story arc. We have had that already for the last 12 years. "Bad wolf", "torchwood" and other things have all been series arcs so why would Chibnalls be some massive story?