Why did my friends credit drop like 30 points?

I still don’t know in depth why. I know one of the reasons was that he was barely using his credit card which i told him to just use it for gas each month and the other was he didn’t have any installment loans mainly because his car bought and he basically went to college for free because of his dad being in the army. but what’s the other reason?
Why did my friends credit drop like 30 points?
Why did my friends credit drop like 30 points?
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