tar -xf is not really special combining short options isn’t uncommon.

Where tar is nonstandard is that you can leave out the -, tar xf is actually how POSIX specifies it. And we’ve kinda come full circle on that one with many modern utilities using a command syntax, you can read tar xf as “tar extract file” just as you can read git pull as, well, “git pull”.

If you want to see a standard command with truly non-standard syntax have a look at dd.