How to judge grade of carbon frame?
There are manufacturers in Taiwan and China that make bicycles for the major brands known around the world, including ons with carbon frames. It's not inconceivable that a brand known for cheap bikes could contract with one of them to make a carbon bike.

The only measurement you could easily make to judge this frame is weighing it. The highest quality CFC frames use a very careful and precise layup procedure which allows minimization of the amount of material used to get the required strength. The workers who carry this out have to be more highly skilled and take more time. Obviously this increases the cost considerably. Lower quality frames use more material as a margin of error against layup imprecision in a faster and cheaper process. 

You or an experienced rider could ride the thing and get an idea of how it feels in terms of stiffness, compliance, acceleration etc., but it's subjective and influenced by the drivetrain and wheels