The only difference is the way in which the array element is selected...

Another difference is that the second one doesn't have a concatenation operator right after print. Using B::Deparse (with -p), we see that it is interpreted this way:

    foreach my($xy) (@$tmp) {
        ((print($_) . ', ') . $xy);
    }
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Remove that dot, and it should work the way you want it to.