They can't know that but it could be true. Dave's poll, FWIW, last night had:
Ellie and Vito 64.55% (4014 votes)
Bobby and Dianne 23.42% (1456 votes)
Layton and Nikita 12.03% (748 votes)
Caveat - much smaller sample size than his usual polls but he has generally been in the right ballpark. I imagine Layton might be a bit higher than that but Ellie was clearly the runaway favourite.
Bobby actually did well last night, though the samba was overmarked and I'd rather not have seen the CC again. I liked that Dianne was so happy for the winners, and hopefully she'll get back to Oz now, see her dad and chill out.