Congrats on not just taking the 5.4% consolation prize!
With that said, 4.2% is still a pretty stiff rate, assuming good credit and a manageable debt load (DTI).
Good news is you can refi ASAP with one of the many other readily-available options out there.
PS: Loan rates are often advertised “as low as…” and heavily disclaimed (credit unions do this too!), and decisioning / pricing on auto loans is generally automated.
Phone agents are there to provide general customer service, and have little or no insight into how the approval/pricing algorithms work.
Good luck with the refi!