I'm afraid I disagree. An OS course needs to at least cover virtual memory, processes and filesystems. Doesn't look like "Baking Pi" does.
That depends on what you mean by "Operating System". Lots of real time operating systems don't have virtual memory or file systems. But I would agree with you that the "Baking Pi" course covers little of what one would typically associate with an operating system, it is much more of a course on low level ARM assembly and interfacing with a frame buffer.
That one is in straight Assembly, but actually quite interesting to follow.