"Postmodern" has it from the linked twitter thread: "they [are] probably confusing LGPL with GPL/AGPL, or are afraid of getting Stallman cooties."
Parts of it being BSD does not mean it is dual licensed, it just means you can remove the BSD parts and reuse them elsewhere as BSD; you cannot just take BSD files and strip out the license as the terms say the license must remain included.
Its correct however that one can not remove the actually license text from the BSD licensed code. Doing so would be a license violation of the BSD license terms #1.
This is the good part about BSD for FOSS projects. One do not need to do any active action to be in compliance with the license. Do changes, add any licenses, and so long the license text on the BSD source code is intact, you are in the green.