Please Help With The Ending

Spoiler Ahead
After Donald Pleasence's character is led away by the men in white coats Jack Hawkins goes through a door which closes behind him. The young boy from the first story comes out followed by a tiger which proceeds to attack Hawkins. If the tiger was real then why was the kid in the madhouse? I was under the assumption he murdered his parents and blamed it on an imaginary tiger and that was why he was there. But if the tiger is real why was he in the looney bin?