Fett knew good and well who Luke was. It's important to understand that Fett doesn't have a heart of gold. He never has and never will. Just because he shot at Luke does not make him a bad person. For instance, do you like Han Solo? Personally, I do not but most ppl do. He is a smuggler and a filthy, lying cheater. Being a bounty hunter is a legal profession throughout the galaxy, but smuggling is not. At the very least, most of Fett's bounties are corrupt politicians or criminals. He is WAY more moral than Solo. Think abt it: Solo smuggles spice (an extremely dangerous drug that is responsible for a ton of deaths all throughout the galaxy) with no regard as to who or what he might be hurting (Boba has a bone to pick with Solo just bc of that), Fett believes that the Jedi are corrupt and have no more right to anything than anyone else (which they are and they don't), Solo's code of ethics (if he even has one) is so loose and inconsistent that he might as well not even have one, you can only trust Solo as far as you can throw him and his word means absolutely nothing to him, whereas Fett will never go back on his word no matter the consequences. Fett may not admit it but his uncompromisable code is the identifying trait of a true Mandalorian. Fett may not be the average person's "cut and dried" idea of a "good person" but I think he's the closest anyone in the entire Star Wars universe has ever gotten. Including the Jedi.