I wrote to Larry about this sort of thing once:

me: The following is from page 75 in the Camel: "List assignment in scalar context returns the number of elements produced by the expression on the right side of the assignment:

$x = ( ($a, $b) = (7,7,7) ); #set $x to 3, not 2

why. how.

Larry on why: Because then you can use it for a boolean value:

while (($a,$b) = somefunc()) { ... }

If it used the number of elements on the left, it would always be true.

Larry on how: It counts them. :-)