Besides the complete absence of any contemporary evidence that MtGox ever sold Magic cards, there's the silence in all McCaleb materials. For example, https://ripple.com/blog/interview-with-jed-mccaleb-inventor-...

   How and why did you create Mt. Gox?

   At that point there wasn’t a good way to buy and sell Bitcoins and I wanted to buy some. So, as a side project, I made Mt. Gox and bought my first Bitcoins there. As the company started to take off, I sold it.

Note what is completely unmentioned there: any evidence that Mt. Gox was made for any reason other than Bitcoins. If Mt Gox was an operating Magic card exchange, isn't that a really strange way to describe its history?