The reason the industry has "tryouts" is to see if the two styles mesh. Normally, a portfolio would be okay in most cases, because a client would be hiring the artist for their work, ALL their work. In this particular case, he is hiring a colorist to color already made drawings. If he hired someone solely based on their portfolio, he'd be taking a risk. Sure the coloring style might look great in the artist's example, but it might not match with his drawings or be the mood or style he needs. He can't tell until he has someone try it out on his own work.

I've applied for many a job like this, and for freelancers, a test page is normal. And sometimes, rarely, they will pay you for that even if you don't get hired. Yes, there are some people taking advantage out there and getting free work, which doesn't work anyway because then a comic would look like it's done with a patchwork of styles. But he clearly says, the test page will likely be something he already had done, and therefore couldn't use anyway.

I think you're being a bit too strict. This forum is for job offers, and this is clearly a job offer.