Small nitpick with the title, because I still find it humorous all these years later, but it's not "Mt. Gox" like Mount Gox, it's MTGOX, which stands for Magic The Gathering Online Exchange, as it started out as a trading platform for that, and adopted bitcoin early as a way to facilitate trades of the cards without cash.
The Wikipedia page agrees with you as well: https://en.wikipedia.org/wiki/Mt._Gox
There's some discussion about potential Citogenesis here: https://en.wikipedia.org/wiki/Talk:Mt._Gox#Possible_citogene...
> More importantly, McCaleb replied to my email. In response to my question "Did anyone ever actually trade card for card or money for card on Mtgox.com?", he replied "yeah they did". I've asked him some followup questions on dates & volumes & closure reason, but I guess that settles that... Does anyone recall the OTRS procedure for storing emails from primary sources? It's been years since I've last done it. --Gwern (contribs) 20:36 17 February 2014 (GMT)
It was literally branded Mt. Gox. In the logo and everything. Also, he had already shuttered the MTG project and simply re-used the dormant mtgox domain.