Windows did run on a 286. Windows 95 might not have but Windows 1 - 3.1 most certainly did.
Well yeah, but that was kind of the whole point. Windows up to 3.1 was fundamentally a 16-bit OS (Win32 extensions for 3.1 notwithstanding,) and thus it was perfectly feasible for it to run on a 286 (though I don't recall if it ever made use of the 286's protected mode - not a lot did, aside from OS/2 and Xenix.) Windows 95 on the other hand was the first real step forward for the OS, using 386 protected mode to provide some actual process separation and memory protection (albeit not very well-handled) in a potentially greatly-expanded memory space.
xeron's point, if I'm not mistaken, was that OS4 is similarily a step forward from OS3.x and is not backwards-compatible for similar reasons. Not sure I agree 100%, but his analogy was sound; buzzfuzz's wasn't.