Most people's idea about a hacker is the movie type hacker. Glasses, hoodie, looking like a regular guy, sometimes even going as far as to wear some insignia that allows them to be recognized by regular people, but the thing is this doesn't happen in real life (wow really never thought of that lol). There are three types of hackers out there, white-hats, black-hats, and gray hat hackers. White-hat hackers are the good guys basically, they are the types of hackers that will breach systems and networks to find weak links and report them to the developers to reinforce the security within that site. The black-hats are the ones who do criminal activities, stealing identities and money online, extortion, you know the likes, and then there's the gray-hats, these types of hackers will either do illegal stuff for fun and then reestablish or return stolen goods just for the sake of it. I would assume this guy who stole $600M worth of crypto could be classified as a gray-hat.
Nothing can "make" them return the money. This guy may have done it, but he wasn't "made" to give it back, he gave it back because he wants to. I mean if I have 600 million dollars in my account, no matter how dangerous it is to cash that out, I would figure out a way, hell I would deal with mafia or other illegal people and find a way to still do that, as long as I can keep that money as it is, that alone itself is a big deal, if I am a bad hacker who wants to keep the money, I can find any way possible.
However at the end of the day this was a good person who gave it back, even if you catch a bad one, they will go to jail knowing that they have 600 million dollars, I would go to jail for the rest of my life if it means I will have 600 million dollars, at least my family would live a great life somewhere they can't be found. This is why nobody can be forced to give it back, only good people would do that.
He's basically a good guy who tried to play with people's feelings and money in the process. Sure he returned the money under his own will, and we'll never know what made him return the money besides the fact that he felt like returning it. But the fact remains that he stole the money first for something, what that reason may be we do not know, but that alone puts him in my book as one of the best if not the best gray-hat hackers out there.