Lists are surrounded by brackets....

Not rvalue lists! Commas, not parentheses, produce literal rvalue lists. The three array references in this variant of that code are a list just as much as in the original version:

my @compass = 
    ["NW", "N", "NE"],
    ["W", "center", "E"],
    ["SW", "S", "SE"],
;
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The difference between the two examples is the precedence of the assignment operator compared to the precedence of the comma operators.