From what I read this is a offline (in device) password manager, as BitWarden is a service (online).

Yep, BitWarden can't handle being offline (storing passwords for ex.).

Bitwarden handles being offline just fine. Like you need to go online eventually if you want to sync your changes but it's not like you need internet to manage your vault.

It lost a password for me when I were offline and pressed "Yes, save password" on the bar dialogue, don't discount the possibility of bugs existing.