Yes, NOR flash was common in these kind of devices and phones until maybe 2005 or so. So you could run code without loading it to RAM first. However, I believe RAM was still needed for stacks and heaps. Writing them to NOR flash sounds too slow.
No, I really do mean that they used the disks as ROM. No writing to it. This worked because you can just put the stack and heap at a difference position in the memory map from the executable code.
