the article's sources have links that don't seem to work, but one that does doesn't seem like it's cooked up nonsense. i'd say more data is needed here and i'm not fully sure what is being suggested.
it does suggest eating a variety of plant sources and that some aminos are provided in excess, but also suggests that under some conditions people can eat a diet of just rice and be alright, based on the measurement of nitrogen availability, and i don't know how that works. though i'm still skeptical of a rice fed diet meeting protein needs in someone who is active.
to clarify: i was not suggesting that vegetarian diets are necessarily inadequate, or that you need to eat mixed proteins at every meal, though was saying as long as they are eaten with a day or so of each other.