According the Wikipedia page he did it as a favor to the creators. They do not have their own Wikipedia page so I have no idea how they know him. The film was pretty much universally hated for virtually every aspect.

Sir Billi received extremely negative reviews from critics and audiences. On Rotten Tomatoes, the film holds an approval rating of 0%, based on eight reviews, with an average rating of 2.3/10. On Metacritic, the film has a weighted average score of 17 out of 100, based on 4 critics, indicating “overwhelming dislike”.