No, it is quite common that you have two different versions of the same frame, one being lighter than the other. There might also be subtle differences in how the frames ride. Usually, the lighter frames have a more involved carbon layup, which means they are more expensive to produce but also can have better properties such as compliance, and can be made lighter. Very often only the most expensive variant of a frame is on sale separately, so it isn’t always easy to find out weight differences between two frames.
Still, to give you an idea, here is a comparison between Open’s UP (= normal variant) and the UPPER (= lighter, more expensive version of the same frame): in size M the frame of the UPPER is 160 g lighter (880 g vs. 1040 g), the fork is 20 g lighter (370 g vs. 390 g). So you save about 15 % in term of weight for the frame and 5 % on the fork, or about 13 %. However, the UPPER is about 50 % more expensive than the UP.
It is very common for companies to have two models of the same carbon frame. BMC’s Teammachine and Roadmachine come in two carbon variants, my mountain bike frame, a Merida, came in two variants, etc. The exact weight savings of course might be smaller or bigger in other cases. So my example with the Open is really just that, an example.
Conclusion: the weight difference is real, but so is the price difference. Is the price delta justified? Depends on your definition of justified. It is almost always better to make a “reasonable” build than an all-out build.