Aren't SEGA and Microsoft both publishers? So a publisher buying a publisher? Sounds interesting at the very least, never heard of such a thing before, nice find there. And I'm not saying it's not possible or anything, I'm just surprised, that's all.
These things happen.
If one publisher has a game in its portfolio, which another publisher would want and that another publisher can afford it, they could buy it out and merge.
Doesn't really happen with "world level" publishers though as they are wealthy enough on their own.