Microsoft didn't invent the flat rectangle. What about the new iOS looks specifically like Windows Phone 8?
They did, however, create a set of design principles for user interfaces for computer applications (inspired in large part by particular pre-computing graphic design styles, but also including particular principles for providing affordances and feedback for interactive applications within that graphic style.)
I didn't mean to suggest that it was, I was trying to suggest a better focus for discussions of whether iOS design was following Microsoft in any substantial way than either "flat rectangles", or even "what bits seem generally similar to Win 8".