Each of those sensors had an arrow that was supposed to point toward the top of the vehicle, however multiple sensors on the failed rocket were pointing downward instead.
It seems amazing that something as fundamental as this was not caught during quality control. Even more amazing is that the design of the sensors permits them to be installed in the wrong orientation in the first place. Even the simplest of mechanical interlocks (such as a notch at one end that must be matched with a corresponding projection) could have prevented the accident.
If the facts don't fit the theory, change the facts. -- Albert Einstein