Clearly there's some component of UEFI that's in firmware, right? I don't really know all the terminology and such here, so please correct my understanding, but -- even if you don't have a disk, you'll get some UEFI bootloader. I seem to recall that some devices like many Chromebooks will have some extensive EFI blobs in firmware partitions, at least some of which is a read-only "get back to factory settings if you really screw up" stuff. I don't see what could stop a vendor from putting whatever they want into a a read-only firmware EFI partition, I'm pretty sure they exist in the wild.