One example was a file extension called .phtm - the best I could guess it meant (and how I thought of it) was "parsed HTML", but that's kind of stupid because every HTML file is parsed. Maybe it meant "proto HTML" because not all of HTML was supported. Maybe it meant "Phil's HTML" or "perhaps HTML". Nobody had any idea. There wasn't an obvious P that related in any way to the business needs or function of the file format.
As a programmer, do you need to know what XML, SOAP or REST mean to be able to use them? Not really. And to give another example, back in the days when I also did sysadmin work and had to deal with both IDE drives and SCSI drives, I wouldn't have remembered what the initials meant, nor would I probably know what the e in NVMe is if I hadn't just googled it even though I've used them for years.
That could be a valid test, but I do a lot of government contracting, and that industry is absolutely rife with acronyms nobody knows the expansion of, as well as names that were chosen because somebody thought they were cool but aren't acronyms, but everyone else assumes are acronyms, so they get the capslock treatment.