That doesn't make LED look very good. However, they lied. The world is full of people that have to tell a slightly bigger lie than the liar before them. 2g/w is the point they started to call each-other out on it.
HID is used at 600w per meter, like an industry standard (1000w over a 4x4 in the states). Seeds are rated as production per meter with that expectation. Good breeder catalogues top out about 650g per meter (1.1g/w) with 500-600 being the usual commercially viable cash cropping strains. Some catalogues are full of 800-1000g claims, and should be ignored. I have done a few, and it's straw.
This situation is evolving. Driven by LEDs making higher yields possible. The catalogue number are probably creeping up. The yields under HID are about 1g/w if you take some care with higher yielding plants. Many home growers are not getting 0.5g/w using boutique strains that can barely manage 0.66g in the right hands.
Gram per Watt isn't a commercial measure. Using it commercially isn't viable. Look in these seed catalogues. It's not there.
I know Mars like many other LED sellers are using Gram/W in sales brochures. It tells a commercial grower, that Mars are in the lighting industry, and can offer no horticultural support.
We do heard some commercial guys to tell us they can get that number. Maybe they use the best seeds and some Co2 to boost the yield.