Hacker News Reader

I think 'private' refers to 'company' and the companies' business model / focus area is 'longevity'.

So they are 'private companies' (private ownership) in the longevity business.

The company is private.

They are working on longevity.

The company is not working on "private longevity"

I think you're reading the phrase wrong.

I think they're referring to private companies.

Private companies, not private longevity

'private' modifies 'longevity companies' not 'longevity'

You’re not an idiot, the title has a typo. As it reads, your first interpretation is correct.

If they wanted “private” to modify “companies” (rather than longevity) it should read: “…raised by private, longevity companies”.

English certainly allows you to have a string of adjectives that modify a single noun without the use of commas. The phrase is simply ambiguous, but there is no typo.