"all college students who drink beer make less than a 4.0 g. p.a. it is obvious then that drinking beer lowers a student's grades." this is an example of someone who believes that

This is an example of someone who believes that correlation proves causation.
Correlation between the GPA of students who drink beer and the GPA of those who don't according to this person will cause the belief that beer is the reason why their GPA is lower than those students who don't drink beer, which doesn't make much sense.