Thanks for everyone's replies.
I will admit that the new business lounge was nice (and much better than the loft lounge that looked over the concourse when I was traveling through a few years ago) - however the "niceness" of the lounge is not really the point of my post.
I did some digging and came up with some info on the Star alliance page.
Here is what that site says - and based on this info, and the logo posted on the sign at the door, I would maintain that since the F side was labeled as a Star Gold lounge, I should have been allowed in to either side.
Star Alliance Gold Customers Travelling in Any Class:
Customers have access to any Star Alliance member carriers' owned lounges with the Star Alliance Gold logo at the entrance.
Customer must present proof of Star Alliance Gold level status via a valid frequent flyer program Star Alliance Gold level card or other valid indication of Star Alliance Gold level status
Customer must also present a boarding pass for travel on a Star Alliance flight departing from the local airport
Customer is entitled to one guest
United Star Alliance Gold customers may only access the United Clubs within the U.S. when travelling in conjunction with a Star Alliance international flight.