And he says, multiple times, in that article that carb number can be lower without ill effect with sufficient protein intake. He's just saying it's easier for most people to just eat 50g of carbs a day than jack up their protein intake.

e.g.,

>However, strictly speaking, any diet with less than 100 g/day of carbohydrate will cause ketosis to develop to some degree (more ketones will be generated as carbs are lowered).

[...]

>In any case, an intake of 15-50 grams per day of carbohydrate will still allow ketosis to develop and those ketogenic dieters attempting to ‘eat as few carbs as possible’ might want to consider that in the context of not only providing much needed food variety (at 50 g/day, even a small amount of fruit can often be fit in) but also in the context of the protein sparing issues I discussed above. Getting to the point, although the physiological requirement for dietary carbohydrates is zero, we might set a practical minimum (in terms of preventing excessive body protein loss) at 50 grams per day. I’d note again that, within the context of The Rapid Fat Loss Handbook approach, carbs are limited to essentially trace amounts; however protein (which makes up the majority of the diet) is set high enough to limit muscle loss.

[...]

>So, summing up mid-article, the absolute requirement for carbohydrates is zero grams per day. However, depending on protein intake, a practical minimum for carbs lies between 50 grams/day (if someone functions well in ketosis) to 100-120 grams per day (if they don’t function well in ketosis). Let me mention very specifically that I’m not suggesting those numbers are a recommended level, I’m simply using them to represent a practical minimum value.