She most certainly was Queen. Her formal style and title after George VI's accession to the throne was Her Majesty The Queen, and she was correctly, though less formally, known as Queen Elizabeth. She was not a Queen Regnant (as her daughter is) but a Queen Consort - but nonetheless a Queen.
The article refers to her as Queen Elizabeth and that is how she was known at the time. There was a need to distinguish between her and Queen Mary, George V's Consort, who was also still alive at that time.
There are plenty of mistakes in this article - but this is not one of them.
You’re right — keeping track of royalty has never been my strong point. But I’m keeping a close eye on the guy in the White House who’s acting like a king.