Getting your butt whooped for 5 rounds is the more likely culprit. From medscape (sources are primary medical peer-reviewed literature):
The diagnosis of rhabdomyolysis can be confirmed using certain laboratory studies.[13] The most reliable and sensitive indicator of muscle injury is creatine kinase (CK). Assessing CK levels is most useful because of its ease of detection in serum and its presence in serum immediately after muscle injury.
CK levels rise within 12 hours of muscle injury, peak in 24-36 hours, and decrease at a rate of 30-40% per day.[65] The serum half-life of CK is approximately 36 hours. CK levels decline 3-5 days after resolution of muscle injury[13] ; failure of CK levels to decrease suggests ongoing muscle injury or development of a compartment syndrome. The peak CK level, especially when it is higher than 15,000 U/L, may be predictive of renal failure.[66]
The timeline of his lab values completely fits with trauma from the fight being the culprit of his elevated "creatine", NOT overtraining - it's far too long after a fight for that to be a likely culprit (although still possible). Admittedly, it's impossible to know for sure from the extremely limited information we have.
Besides, if he was wary of overtraining before the fight, don't you think he would've gotten levels BEFORE the fight? Somebody mindful of such a thing surely would have been aware of their levels beforehand.