As kennethk and ikegami point out, the crucial thing to realise is this snippet from Matching in list context:

If the /g option is not used, m// in list context returns a list consisting of the subexpressions matched by the parentheses in the pattern, i.e., ($1 , $2 , $3 ...). (Note that here $1 etc. are also set, and that this differs from Perl 4's behavior.) When there are no parentheses in the pattern, the return value is the list (1) for success. With or without parentheses, an empty list is returned upon failure.

That's the motivation for the seemingly strange @array = $string =~ m/$regex/ pattern (which parses as @array = ($string =~ m/$regex/)) in kennethk's post.