Informal offer before any recommendation letters have arrived

A person I know applied for a time-limited position (i.e. a post-doc) somewhere in western Europe. Xe gets invited for an interview. The next day, xe receives an informal e-mail, We will recommend HR to send you a formal offer.

However, we are still waiting to receive recommendation letters from your references before we can do so.

And I thought the content of recommendation letters were essential. In this case they are apparently a formality. Is this indeed very unusual, or is it more common than I think?