The report actually admits that it's skewed towards online behaviour.
I find it puzzling that there are conclusions about the fraction of the population that attend theatre. The report says "A large majority (76%) of the UK population has been to at least one theatre show [...] in the past three years", but there's nothing to back up that claim and no mention of its origin, which is odd considering that other claims are accompanied by charts.
I'm also annoyed that there's a "who do you go to the theatre with?" section but it doesn't include "nobody". I do not believe that a randomly chosen population of 1818 theatregoers didn't include any singles, so either they haven't bothered to include them in the results or they used a question along the lines of "when you go with other people, who do you go with?"