I'm aware of the importance of clarity. If I were golfing I would have done something like

my ($x, $y, $z) = split(',', "$_,,");
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but this was the most natural answer to me. The problem, as I saw it, was "sometimes the list returned by split is too short, and I want empty strings to fill missing places at the end," so the most natural answer I saw was to add items to fill it out.