Dude's really just be saying nonsense that technically works on paper, but makes no sense if put to practice.
Like, what's all that random blather about the rice sweetness? As if any plain old sushi rice don't have that sweetness?? The konbu being added for some depth to the taste is one thing, but to make sushi rice you're have to add salt and sugar together with the vinegar anyway. Whatever subtle sweetness you get from the natural taste of the konbu is gonna be lost in the sugar.
Pretty convinced this bro had no idea about the salt and sugar and thinks that you just put plain vinegar into the rice.