Chinese DDoS? Somehow I don't buy power going out at a server farm.
And why would GitHub not disclose that it was a DDoS? They were very forthcoming when there actually _was_ a Chinese DDoS last April: http://arstechnica.com/security/2015/04/ddos-attacks-that-cr...
And in a DDoS, the service typically becomes slower and slower until it reaches the point where only like one in a hundred requests succeeds. With the GitHub outage, it died fairly instantaneously, and it was completely 100% dead. There was no timeout as the servers tried to respond -- the "no servers are available" error page loaded instantly every time.
You should read more about server farms.