Multiboot was invented long before Linus had his kernel up to v1.0, while IBM and M$ were still partners in OS/2 development, for having DOS and OS/2 bootable from and in separate partitions on the same or separate HDs. Dual boot, released in conjunction with multiboot, was for making both DOS and OS/2 bootable from the same partition.
I’ve been multibooting around 25 years, since long before Win95 and OS/2 Warp.