Having the Star Gold-noted card would have gotten you and guest in (I'm assuming you were travelling in coach for all this to happen in the first place) w/ your LH BP. PC card didn't work because you were not on CO metal. If you were on Continental flight, you and guest are accorded access.

They are strict about having a physcal card (vs claiming to be one and asking them to look it up).

The admittance rules are listed in CO's affiliate lounge section (incl. the requirement to be on CO flight). The interpretation by Lounge and CSR were correct.