A lot of Predator superfans are really into the 'Yautja' concept with strict codes of honor and such. More like samurai than big game hunters. I don't think that really jives with the original movies tho.
The Predators in 1&2 don't fight fair. They hide out of sight, invisible to their prey, killing them from afar with advanced weaponry that doesn't even require aiming. In the first movie the Predator only goes hand-to-hand when he isolates a victim and they can't really threaten him. The hunter in P2 is a little more bold but he still favours cloaking for his attacks and still greatly outclasses his victims. They're also sore losers, turning to self-destruct when they think they're about to lose, trying to take their foes down with them rather than take the L.
The honor code idea only really relates to not killing unarmed/pregnant/sick enemies and awarding Harrigan the pistol. This isn't necessarily because it would be un-chivalrous imo though. It's because there's no challenge in the kills. If you're at max level in an rpg, do you go back to the starter zone and kill level 1 rats that can't even chip at your HP bar, let alone maybe get lucky and actually wound/kill you? I don't, because it's boring. No risk at all. Risk is what makes the hunt exciting.
As for the pistol, yeah they show a kind of begrudging respect but it seems kinda like it's specific to that one elder, because no other pred to this point had any qualms about turning their death into a murder-suicide when they thought their foes might actually defeat them. Also worth pointing out they don't exactly give Harrigan a chance to get clear before they launch their ship and very nearly crush/incinerate him.
The Yautja concept makes me roll my eyes tbh. The original Predators were trophy-taking slasher villains who saw us as little better than animals, equipped to pose some threat but not equal or worthy of respect as more than wall decorations.