Do you even know how the stars work? That guy practically cheated, and I'm not joking or shitposting.
1st star: Great achievements in your own field.
2nd star: Have an apprentice who earns their own star.
He was a Head Hunter. He scouted talented people and helped them fulfill their potential. Do the math.
This doesn't even consider that achievements aren't necessarily combat related. Actually, more often than not they aren't. Even then, people who earn combat related stars can still be pushovers. That single star Bounty Hunter got off-paneled by Hisoka like it was nothing. I bet that if a criminal is barely above civilian grade and doesn't even have nen, then if they're infamous enough a Bounty Hunter can still get a star for taking them out.