

If you use a VPN, you’re always connecting to the same IP
No, you’re not. A VPN provider can have hundreds of thousands of IP:s.
which is unusual
OK, but not unheard of. And even a dynamic IP might remain the same for months, if not years, depending on the operator.
would tend to indicate VPN usage
No, it wouldn’t.
Well, the client code is liensed GPL 3.0 and server code is licensed AGPL 3.0, and those are both FOSS licenses. There are some additional commercial components licensed under a non-FOSS source-available license, but those are not required for the basic service. I guess you can’t use the Bitwarden trademark either. I would still consider Bitwarden FOSS, although with a slightly limited (but not crippling) scope of the term “Bitwarden”.