There is a possibility that they were ALL males, but not all of them were wearing their courting colors. I only say that because not all of the males I've caught in recent trips were heavily blackened up, even the ones caught right against the bank.
Then again, since they don't ALL spawn at the same time, there is the possibility of catching blackened males plus females w/o eggs in the same trip. And the males do stay on the nest, guarding eggs/fry, long after the females have done their duty ... so, they may still be colored up.
The only way I know when the females I catch are done spawning, is when egg sacs are present but don't have much left in them. Those that are male, dark coloration or not, are easily identified by the white milt sacs.