To amplify a bit: The original used x twice. Only one of them was evil. Note that the best WTDI may be:

my $matrix;
{
  my @row = (0) x $width;
  $matrix = [map {[@row]} 1..$height];
}
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OTOH, the most perlish way to do it is probably just my $matrix;, and letting perl autovivify the rest when it's created. I assume that dws had a reason to not do that, though.