This is a scalar assignment, and the right side is evaluated in scalar context:

$foo = ...
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These are list assignments, and the right side is evaluated in list context:

($foo) = ...
@foo = ...
%foo = ...
@foo{LIST} = ...
@foo[LIST] = ...
() = ...
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What the match operator returns depends on success of the match, context, presense of capturing parenthesis, and whether there's a //g flag. See the doc for details.