This is an example of stereotyping.
A stereotype is an over-generalized belief about a particular category of people. Stereotypes are usually developed out of prejudices, wrong kind of education or social environment.
Stereotypes are generalized because they assume that the stereotype is true for each person in the category. Most stereotypes are based on gender, age, sexual orientation or nationality.
Mr. Easton has probably seen some people with longer hair using drugs and he developed a stereotype based on his personal experience. It does not matter if he only saw a few examples of such behavior, he projects his experience over the whole population of people with longer hair. His judgment is unjust and not based on any proven facts.
