To some extent, it is a style since it's a certain way you draw something. But professionally, it's encouraged for people to not imitate it if they aren't primarily going into the manga industry and are in a Western/alternative market. It'd be classified as such in countries where comics aren't nearly as popular and manga is more popular.
For people who aren't planning to be artists at a professional level/degree type of level (as in beyond online clients with corresponding media platforms), it's definitely a style of some sort. Just as the Adventure Time super simple style is a style (and often very imitated one).
A lot of artists tend to start trying to imitate it fully but eventually break away from that and develop their own style, like semi-realism or a cartoon style of their own.
The industry is already hard enough to find occupations from even if your style is realistic/non anime. Unique styles are emphasized and homogeny above all else seems to be rather discouraged. Unique styles are frankly more prrofitable than an anime styled one (though ones incorporating elements of it into cartoons seem also acceptable). If they emphasize that such a style isn't acceptable or has a higher likelihood to not receive as much clients, it's because the manga/anime style is hugely homogenized and rather difficult to get a unique style from it. Manga artists have also been leaning away from the once-popular anime style of big eyes and sparkles and crazy hair styles (YUGI) and seem leaning more towards at least a kind of semi realism sort of style and less button noses.
It is a style, but industry wise, I understand why it isn't and shouldn't be considered that way. Half of deviantart users draw anime style. And oftentimes look the exact same.
