You are not guaranteed an upgrade from a Minivan. They didn't even have to offer you an automatic version. The rules state it's a one-car upgrade and is not eligible for
vans, luxury and Prestige cars and rentals longer than 14 days. As a PC member, you hope you're treated a bit better than the huddled masses, but this is entirely discretionary.
Glad to hear you were treated well on the return though. That was certainly nice of them to waive the fuel charge as it was not required. Happy it worked out for you.