The quotations say nothing of the sort. A vendor could provide a dual-boot device providing they have an Android bootloader signed with Microsoft's signing key, which is a service that Microsoft will be providing.

A more open question is whether any of the existing Linux vendors will be doing this. Fedora is willing to use Microsoft's signing service for x86 because users will be able to disable the feature or enrol their own keys. We're not willing to do that for ARM because users won't have that freedom and so wouldn't be able to replace components like the kernel.