the usual and customary way to write that code

Yes - I would always write it as my ($x, $y).
It was precisely because it was not written that way that I noticed it as odd!

WRT brackets in the split, I used to include them but have moved away from doing so as I feel it is easier to read without them. There was a time when I used brackets for virtually everything, including print statements! I do use them where they are not strictly necessary any time that precedence might be in less then obvious.