Yes. The core target audience of the article is likely unilingual families who will put their kid in French/Chinese/whatever classes to give them a leg up for Harvard admissions, 15 years later (or, in the NYTime's subtle language: "parents who want to give their kids a bilingual boost").

Obviously if the kid only speaks the language in the context of a classroom, true fluency will never be reached. In a realistic context, true multilingualism is very achievable, and not particularly exceptional throughout most of the world as many other commenters have pointed out.

Implicitly you appear to suggest multilingualism is easy to achieve in [almost] all contexts?

Where parents are monolingual, and the pervading culture is monolingual then there's little opportunity for immersion and few people from whom to learn.

I'd guess that the kids you knew growing up were speaking english in school and another language at home, so they likely don't develop the vocabulary and grammar in their 'home' language that they might have if they were studying it every day in school. From the article regarding kids from bilingual homes who speak english in school: "... they didn’t go to school in Spanish, they don’t read books in Spanish, and when you actually measure the size of their vocabularies, or the grammar they understand, or the coherence of the narrative they produce, they are not as proficient as they are in English".

(Or perhaps I just have a very skewed sample set and even "regular" bilingualism is rare)

Idk. Overall this article didn't sit well with me, for more reason than one (https://news.ycombinator.com/item?id=14830685).