it's so confusing that the order changes when adding IDENTICAL strings to BOTH filenames. Is this really how it's supposed to be?
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Linux is a family of open source Unix-like operating systems based on the Linux kernel, an operating system kernel first released on September 17, 1991 by Linus Torvalds. Linux is typically packaged in a Linux distribution (or distro for short).
Distributions include the Linux kernel and supporting system software and libraries, many of which are provided by the GNU Project. Many Linux distributions use the word "Linux" in their name, but the Free Software Foundation uses the name GNU/Linux to emphasize the importance of GNU software, causing some controversy.
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I don't know the exact reasoning for it, I would guess it's because '.' is also used to delimit file types "A book on the.pdf" < "A book on the pdf.pdf" or "Book.pdf" < "Book sequel.pdf"
I guess your confusion has in part to do with reading digits as numbers, but within a string they are part of an alphabet, every character stands on its own and has no relation to the characters around it. There is no difference between "5 1", "5.1" and "511" you just pick an ordering of the alphabet and then sort each character accordingly.