The Distinction btwn "Company" and "Corporation" is not complicated

Why do so many people including the IRS and now the U S Supreme Court continually refer to unincorporated LLCs as "limited liability corporations"?  To wit:

" As a part of the scheme, respondents invested in various stock warrants through newly created limited liability corporations (LLCs), which are also respondents in this case."

-Justice Scalia, Arthur Anderson LLP v. Carlisle, 2009 US LEXIS 3463 (May 4, 2009)

There is clearly a flaw in the Harvard Law School curriculum.