When I read the court order, I had the same thoughts you expressed. I would speculate this involves, not a Mueller investigation, but a Justice Department investigation of the Uranium One matter. Uranium One was based in Canada but since 2013 it is a wholly owned subsidiary of the Russian state-owned nuclear corporation Rosatom. Of particular interest would be information about sale outside the United States of the uranium acquired here as well as any payoffs made to U S officials or the Clinton Foundation.
I thought Rosatom was owned by a billionaire oligarch dude. I could be mistaken. I am thinking that that is wishful thinking. I am thinking it has more to do with one of the companies the lawyer Cohen was dealing with involving that “free $50 million apartment” gift to Putin. Even though, as I read the story, that deal had zero to do with Trump (it was Cohen trying to leverage his connections and license his name, not built or financed or managed by Trump personally). But against as I read that story Cohen and the other partner were trying to get Russian banks to finance it and Russian engineering firms to build it. So could be one of those...
Just throwing darts in the dark here.