So simply being expensive is what makes something luxurious? I thought it had to do with the quality and the experience it provides.

IMO luxurious food would be made from high quality ingredients and have an appealing presentation and an appealing consumption experience. And sure, to do all that would made it expensive, but expense is the result of luxury, not the cause.

Just because someone decides to charge a lot for some crap doesn't make it luxurious IMO.