When someone gets notified by their monitoring system that a server was unavailable (because it rebooted) they might investigate and see that the IPMI logs don't mention power loss

Power failure would require both of the power feeds in the DC failing simultaneously and would be easily verified by contacting the DC and asking if they had any power outages reported at the time. Of course there are cheapskates who don't go for redundant power supplies so it's possible but would be indicated in the IPMI logs