There is a reason why people keep arguing about this seemingly semantic difference.
To anyone who watched more anime than a handful of shonen fighters, the writer's premise, that anime is an art style, and a specific type of plot, is clueless at best and offensive at worst.
Cluelessness is acceptable, it's just like grandma calling the PSP "a nintendo". She just doesn't pay attention to details, so she calls everything that is held in hands like a gameboy "a nintendo". Likewise, some people don't pay attention to the genres of anime, just see a few minutes of Naruto, and assume that Avatar must be the same thing.
But continuing to ARGUE that the anime fans are the ones who got it wrong, and making up theories about their snobbery, or whatever, instead of just accepting that anime fans know more about what is and isn't anime than random people, is arrogance.
It's a bit like telling to console gamers Diablo III should be called a console game, because it's so simple that even if it's technically released on the PC, it's much more similar to console games.
It wouldn't just incredibly dismissive against console gaming (assuming that all PC games are inherently more complex than them BY DEFINITION), reducing it to crude stereotypes, but also inaccurate.
The article author's claimed goal is just laughable, he is trying to save anime fans from "narrowing down" their medium, while his own understanding of the medium is ridiculously narrow. He would add Avatar to his definition of anime, while at the same time, exclude Baccano, Usagi Drop, Haruhi, Welcome to the NHK!, Kimi ni Todoke, Nichijou, School Days, and Bakemonogatari from it.
It's a bit like warning a frenchman to the dangers of French couisine, on the account that humans need other nutriments than frog meat, so recommend them to eat more hamburgers:
you are not helping, your own stereotypes are creating the problems that you are trying to solve.
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