I disagree (at least following German law):
As long as no author has signed an CLA, they stay the owner of the intellectual property and their portion of code may only be used respecting the original (here BSD) license.
Every link in the post you mentioned also refers to contributor agreement as a component for the "rights ratchet".
But in practice I'm in doubt whether there is any chance in sueing Redis... so in consequence it makes no difference.