I saw that as well in a video linked in another thread, though it did not go into details and the video maker did not seem up to much else they would have checked that. If it is a nice torrent of separate files I guess there might be scope to have a peek but eh.
That said while the existence of these leaks at all speaks to a lack of security somewhere along the line I would be stunned if it contained the private keys for the retail 360 dashboard/kernel or userland games/code. That is the sort of thing you keep locked up very tightly and have all your devs send you files to sign, and check (and check before they sign in case it is an all 00 file and that gives the key away as all 00 files do bad things to keys in many crypto formats -- see 3ds XOR keys for a more basic one there).
If said devs need keys for what they do you have a separate set for development boxes, high end reviewers (IGN and what have you that get stuff months ahead of time) and developer kits. That way if the dev stuff leaks then not ideal but realistically no big deal as dev boxes are only really in the hands of developers.
This cache of info then more likely to come from some kind of government or big company source code vetting (Microsoft lend out the source code for Windows, Office, Visual Studio and the like to very big companies and governments all the time before big contracts), outside security testing, lawsuit discovery maybe, maybe a backup vault somewhere, possibly an employee with an information hoarding problem (engineers are often like that -- just in case/might be useful/saves downloading it again/... , and frankly it has saved the day on more occasions than people would like to admit)... most of which would not need nor benefit from having private retail keys.
If anything is in there it is more likely to be the public stuff we have stuck into the likes of le fluffie and whatever else we use to poke about in isos, XBLA, DLC, saves, hard drive images, and the like for years and years now, or maybe space for some user keys for things like saves and profiles for use in tests.