Nothing in the article suggests the child was not under control.
Was the child running around? Screaming? making a ruckus? Knocking things off the shelves? Making a scene?
The child was playing near a mirror.
From the article: apparently playing near the 5-foot-tall mirror
The mother was not watching him.
From the article:she was about 5 feet away from her son when she heard a loud crash.
If you aren't SEEING what your child is doing, that's not control