My guess is it's a form of ruellia. I am very hesitant to buy from any source who doesn't include a botanical name when they label or advertise a plant, especially mail order ones, and super especially those who do not include an untouched photograph, far enough away to show the foliar part of the plant.

If it is a ruellia, then I would be suspect of its winter hardiness in any but the warmer zones. I have kept a small line of seed-started ruellia alive in zone six, I can't remember the cultivar. It remains green only in the protection of my overwintering house. It dies back to the ground in winter in very protected outside spots and I'm surprised it even does that well. It doesn't ever make it to shrub status.

Your "Japanese" petunia shrub may have completely different qualities if it is a ruellia, and I'm sorry I can't give you a better answer. Hopefully somebody else here can. If it were at all mainstream in my area as a hardy overwintering plant, I would have prolly seen it in my sourcing catalogues.