Yeah, by definition MRSA is resistant to that generation of penicillin drugs (Methicillin Resistant Staph Aureus, vs MSSA which is Sensitive).

Better hygiene wiping down / cleaning BJJ/wrestling mats would probably help. But it's just really horrible luck. Millions of kids wrestle every year and rarely you'll get a superficial cellulitis that doesn't cause complications and is easily treatable.

I suspect him being super healthy led to delaying seeking help. We see this sometimes with kids who are super resilient and eyeball well right until they suddenly decompensate and are at the brink of death. Combined with what I presume is a particularly resistant strain that persisted despite initial course of empiric antibiotic treatment.