Gitlab has demonstrated its commitment to keep the core of their product, though limited in features, free and open source. As of now, BW's clients cannot even be compiled without the proprietary SDK anymore.
None of that makes Bitwarden not open source. Not only that, they specifically state this is a bug which will be addressed.
I would go as far as to say that Bitwarden's main competitive advantage and differentiation is that it's open source. They would be insane to stop that.