A few ideas--
First, lots of bishops, Anglican and Catholic, wear black shirts at times. So it could very well have been +Ackerman or maybe the Episcopalian bishop from Davenport.
In Orthodoxy, a pectoral cross can be given to (whatever they call) an archpriest, so I wonder if it might be a privilege of certain RCC monsignors, too.
Also, it might just be a Lutheran pastor. Lots of them wear collars, and many of them also wear pectoral crosses, since the LCMS doesn't have bishops and in the ELCA the episcopacy just doesn't have a strong history and the perquisites aren't exclusive to them (except the purple shirt and ring, which some of them don't wear).
There's also the outside chance it was an Independent Catholic/Independent Anglican/Independent Orthodox bishop, but that strikes me as a pretty slight chance.