Here is the code in question. Basically, it's a source-available, but not FOSS internal SDK, with the following language:

The password manager SDK is not intended for public use and is not supported by Bitwarden at this stage. It is solely intended to centralize the business logic and to provide a single source of truth for the internal applications. As the SDK evolves into a more stable and feature complete state we will re-evaluate the possibility of publishing stable bindings for the public. The password manager interface is unstable and will change without warning.

So I think the "bug" here is in not linking the original repo in the NPM package, and there's a decent chance that this internal SDK will become FOSS in the future once it stabilizes. That said, it's currently not FOSS, but it's too early IMO to determine whether Bitwarden is moving in a non-FOSS direction, or if they're just trying to keep things simple while they do some heavy refactoring to remove redundancy across apps.

Given their past, I'm willing to give them the benefit of the doubt, but I'll be making sure I have regular backups in case things change.