Hi, org-roam-bibtex-mode should be on to make Helm-bibtex use Org-roam. If it’s off then Helm-bibtex will use its own note-taking facility. You can call this command interactively after Emacs startup or add (org-roam-bibtex-mode +1) somewhere in your config.
In Org-roam v1, org-roam-bibtex-mode was usually called upon startup through org-roam-mode-hook as soon as Org-roam was loaded. The corresponding line was nevertheless required in the config as in :hook (org-roam-mode . org-roam-bibtex-mode). In Org-roam v2, org-roam-mode is not longer a minor mode, so doing so makes little sense. Instead, one can put (org-roam-bibtex-mode +1) in the :config section of use-package org-roam:
(use-package org-roam
:init
(setq org-roam-v2-ack t)
...
:config
(org-roam-bibtex-mode +1)
...)