Factual error: When John is talking on the phone to someone who found a dog, he says something about Odie not being a hound dog, and how sure he was. Odie is part wirehair Dachshund (you can look it up - plus I own Dachshunds), which is from the hound breed.
Factual error: Garfield enters the train control room at Los Angeles Union Station when the only employee in the room leaves the room. There would always be someone in this room when the trains are in operation.
Answer: He's a cartoonist.