Lots of folks gave reasonable explanations of what the right answer might look like, but in case you're wondering what was wrong with the original: The "values" for foo and bar actually got flattened out into the list itself. So what you wrote was equivalent to

my $primaryFeatures = {
    'foo', 'fool', 'food', 'foot',
    'bar', 'barricade',
};
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which is equivalent to

my $primaryFeatures = {
    foo => 'fool',
    food => 'foot',
    bar => 'barricade',
};
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which is why the (food, foot) pairing came out.