Guess I can't edit posts yet ...
but let us know what you find out. I was reading the other day that the green sunfish are much more prevalent in first-order streams - ie the small feeder streams that don't themselves have any real tributaries. I guess green sunfish are actually not native to the area, and they've found a niche to exploit in the very small first order streams where there are limited predators, and not as many competitors for their food supply.
So if you know where they were caught, that might be another clue - the smaller the stream, the more likely it is to be a green sunfish, at least statistically.