The story linking Thomas Sangster to the Tintin Movie first appeared from what I can tell in the British press in the form of a story in the Daily Mail that later gained slightly more credence when it appeared in the better thought of Daily Telegraph.
The Telegraph wrote “Thomas Sangster, 17, who played the role of Liam Neeson’s step son in Love Actually, had originally sent an audition tape to the Hollywood director hoping to snare a role in The Talisman, a project which never got off the ground
Instead Spielberg realised he had found the boy who could play Tintin, the young adventurer created by Belgian cartoonist and writer Georges Prosper Remi, better known by his pen name of Herg