Bad Cat??

I have a 23 WRX Limited. My check engine light started coming on a week after I bought my car. I bought it with 2,900 miles. This week the dealer was finally able to diagnose it as a bad front cat. They said warranty would cover it but because they're covering it so early in the warranty period that if it happens again they likely will not cover it again. Is this normal? Also how the hell can a catalytic converter go bad so early? I've used nothing but 93 since I got it so it can't be the gas. Any thoughts?