So Disk (HDD) and Cloud is fine. Two HDDs (spinny platter style) would indeed fail the test. If you want to argue it you could probably get away with different manufacturers or different batches but I'd prefer my backups to play nicely with the rules rather than try to avoid them! Far-fetched as it is but lets say for example you have a power surge that takes out your external disk (is that even possible?). Chances are high whatever did that would also do that to your other disk. Or maybe a wall caves in and decimates your PC (or you just sweep the desk somehow and knock everything off it. Maybe the desk has collapsed) - The spinny disks may be destroyed if they are both hit hard enough. Mixing an HDD and SSD, the SSD would probably be more hardy against shock damage.

From another comment I made in this thread somewhere "I consider "cloud" as its own media type to avoid the pedantics of me storing files on a spinning disk and the cloud provider does too. Chances are they have server grade disks and their own backups [so it's different to just a raw disk]"

Edit: I use too many brackets here. I am going to attend my next available parenthesis anonymous support group.

Sometimes, when people buy multiple drives at once for servers, they wind up with drives from the same batch. If the drives are subtly defective, and if they're always run under identical conditions (such as in a RAID array), then I've seen multiple drives fail within days of each other.