Just playing the odds. There are a few attributes of a mass/angry/planned shooter that are more common than others.
One reason would be that the shooter may have used the word “normie”
Urban dictionary:
normie
A person who does not have a mental illness such as bipolar disorder, schizophrenia, mood disorders, PTSD, depression or any similar mental disability. “Normie” is a reference to those who are a part of the mainstream culture; the 97% of the population who do not have a mental illness.
That is true.