According to MS' blog post, this is based on the current modules proposal that the committee is working on. Isn't Clang also following the same proposal?
By pursuing implementations of different proposals the committee hopes to converge on a best compromise design incorporating lessons learned from trying them out in practice.
Slightly more info in this write up of the Oct 2015 meeting https://botondballo.wordpress.com/2015/11/09/trip-report-c-s...
The blog post is just oddly written to make it seem like the proposal MS has implemented was approved. Not sure why it was done, but it's confusing.