I'm not certain, but I think it's their way of saying, "We don't have any of that crufty Perl you used to see on those awful 'hotscripts' type sites. We only use the good stuff around here."

Because Perl is a multi-paradigm language (supporting OO, functional, and procedural, and most Perlmongers use a little of all three in any given program), some folks consider it worth mentioning it when the paradigm they use most is OO. I'm a little suspicious when I see explicit mention of OO Perl, as I have to wonder if that means I couldn't use functional Perl idioms (which are often quite nice) if I worked in their shop.