Edward Oliver: the calculation was done offline with a separate bit of software and the fact that answers the question added manually later. It isn't done in real time hence the lack of reasoning when you ask the question.

Although the knowledge base is incomplete it does have fairly comprehensive knowledge about notable people, places and events and over 300 million facts so we stand by the calculation.

You can see the kinds of facts which contributed to the answer by asking questions like

what happened on 20 june 1976?

http://www.trueknowledge.com/q/what_happened_on_20th_june_1976

which should give you a feel for how unusually uneventful 11 April 1954 really was.