Whether or not you believe the student’s assertion to be correct, the fact remains, that the story was brought to the attention of the news station by a student who was presumably an eyewitness.
If this dog was so dangerous, why did most of the high school students remain outside when they could have entered the building in safety? Why did they ignore the police officer’s advice to enter the building if they were convinced that a dangerous animal was running amongst them?
The same reason people crowd around a brawl that breaks out or stand and watch a raging inferno. People get tunnel vision and become fixated by these types of events. The thought that they might be hurt never crosses their mind. I have seen it time and time again. The only time people really scatter is when gunfire breaks out.