The only reference I could find by @ChipMixer is stating chipmixer.io is not their main domain. But there is nothing stating that the .io version does not belong to them, so I am assuming that ChipMixer.io is, in fact, owned and controlled by @ChipMixer
We were under DDoS attack. Tor service was not affected.
They probably do own chipmixer.io but, if they do, it's probably just to stop anyone from doing a phishinng attempt with the domain name.
I think .IO needs less information than .COM does when it's registered.
This being said, I wouldn't advise using anything other than the official chipmixer.com and the official .onion domain names as using anything else would just be foolish. They may have the .io name in case they need to move from .com if they get DDoS attacks on the main site.
(chipmixer.net and chipmixer.org appear to be owned but parked also - not sure who owns those).