It's up to the linguistic community to decide that, if their variety should be considered a "dialect" of something else or a "language" on its own. Linguists already gave up that question, it's more useful to talk about varieties anyway.

And it's the same deal with Galician versus Portuguese, with a difference - "Scots is a dialect of English" threatens Scots, but "Portuguese is a dialect of Galician" doesn't threaten Portuguese (it threatens Galician instead).