Thanks for visiting! TONMO is the world's greatest online cephalopod enthusiast community, with interactive content going back to May of 2000, and a biennial conference. If you'd like to join in on the fun, become a TONMO member -- it's easy and free. You can follow us on Facebook and Twitter for more cephy goodness.
I think the fact that they list octopus under fish rather than invertebrates is a sign that they are pretty lacking in basic knowledge.
This pic is sort of small, but I agree that it looks like briareus to me, too, from the blue color and the webbing, but it's sort of a weird camera angle and octos often look different out of the water like that.
I'd say they just put a picture of an octopus to represent octopuses in general, not the specific species they sale, as they probably list every octopus they sell that isn't a blue ring as a vulgaris, not unlike just about every other dealer.