I question the quote text; An operating system is case-agnostic--it is not usually case sensitive or insensitive. Instead, the command line shells and/or file system drivers are what make case matter or not.
And even then is is not that simple: Computers are numerical machines, not textual. The signals and data all have numerical values associated. Text usually uses the 7-bit ASCII code (in 8-bit groups, so the 8th bit is always 0 in ASCII. Unicode, ANSI, etc, complicate this even more.), where upper and lower case codes are different. Here are the codes for 'A' and 'a' (in binary):
At various levels (kernel, shell, files system driver, CPU, and others), the numerical values are case agnostic since there is no such thing as an upper-/lower-case 1 and 0.
Also be aware of the concept of "globbing". Globbing is the idea of using '*' or '?' to "match" anything--even nothing--in different scenarios and rules, depending one which glob character was used.
In a typical Unix-like shell, such as Bash, the shell will do the globbing: in
ls *, the shell will expand the '*' with a list of matched filenames, before starting the
ls command and pass it the list of matched names, not the '*'.
A typical "msdos" style shell will not do this. In this situation, the
cmd.exe shell would start the
ls.exe command (assuming it exists!) and pass it a single '*'. It is then up to the
ls.exe command to handle the expansion of '*' according to it's own rules.
Add in the file systems... EXT (Unix) file systems are case sensitive. FAT file systems are case insensitive (look at an old FAT floppy image--the filenames are stored using UPPERCASE ASCII), which is complicated more with FAT32 and LFN (long file name support). And NTFS, which tries to bridge the gap by being both--NTFS is generally case-preserving while ignoring case when it tries to match a filename (remember as well, the filename is stored as a sequence of numerical data).
In the example given,
ls te*, the bash shell gives you additional options. For example, try
ls [Tt]e*, and it will match both 'Test' and 'temp', but not 'TECH'.
As you can see, the situation is very complex. And the exact question asked about the statement given is also a complex situation, further complicated because the statement is questionable without additional qualifications and context.