Yes, they most assuredly can distinguish people from one another. I originally thought it was due to the food container but they recognize me without it. They can distinguish strangers, friendly and unfriendly people, family members who don't like them and family members who do, dogs which are safe to go near and dogs which aren't, cats which they can steal food from and cats they'd better not, etc. My sheep also recognizes which cat she can bully and which cat she'd better not, which dogs are safe and which aren't, etc... I believe this is normal cognition for any animal, since no creature which cannot tell friend from foe, harmless from harmful, would survive to pass on its genes. It's normal for any animal to adapt to its surrounds and learn which other animals are harmless, etc.
About the pooping, birds in general have faster metabolisms than us. If they're quick to process the food but it's still shown in healthy poops, that could be considered a sign of health. Even with humans, the longer it takes the more likely the body is reabsorbing wastes and toxifying itself. Some doctors used to tell people it was normal to take up to two weeks to poop! Various things can slow down digestion and various things can speed it up again, and it's good to know what they are. Often a sick bird will recover with a slowed down metabolism which needs correcting.
