From the article
The total content per Mung bean rose on the average from 25% in dry seed to 37% in the (dried) sprout.
I can't see that it's possible for the actual amount of protein to increase, but, like Tom suggested, I think what has happened is that most of the carbohydrate has burned off to fuel the sprouting process, so the percentage of protein is higher.
Very roughly, protein would start off as 25% and carbs would be around 60% with 15% of summat else.
But if half the carbs burned off, then the same amount of protein would now form 36% of what was left, if the
water content is ignored.
I have to watch my carb intake, so sprouting my beans is a good way to drop the carbs.