You don't figure something out. That would be too generous a description of what happens.
The thing about these men who keep turning up to challenge the dread dark knight is, obviously, that the fella presents them with a target.
It's not his fault, but wherever he goes is liable to become the stage of some duel or other, because as soon as anyone gets wind of his presence then every ambitious sod in the region will be jumping up to test their luck and their skill at arms against him. Worst still, he almost never kills his opponents outright, even though he could, so they have no real reason not to try and then even come back and try again. What's the risk? A few bumps and bruises, perhaps a broken bone or twisted ankle at the worst? Meanwhile, the reward would be the hand of the princess.
And it's not as if the dread dark knight just goes everywhere constantly advertising his presence. Sure, he wears a lot of cloaks and hoods and armor, but all things considered you've seen him do a lot to try and make it difficult to actually spot him. He changes his cloaks often, has a few different masks and helms he wears, and even marching around in full mail is not that uncommon in Drakesmeet or Goblin Town, where the king is always sending men to go "enforce order" (read: rough people up to remind them who's in charge). Ostensibly it's all to deal with the necromancers and their human trafficking rings, only most necromancers don't traffic humans anyway, it's usually goblins or orcs or ogres who are easier to disappear, and the only armored human you've seen actually get into it with Kroroban the Unearthly or Sudrakthad the Dire is the dread dark knight.
So you can't even go up to him and be like, hello dread dark knight, have you perhaps considered downplaying your existence so as not to attract the attention of gloryhounds and ne'er-do-wells? Because insofar as that is actually possible, it seems he does.
You don't even have any applicable tips. You're a goblin potter, not a master of disguise.
It seems likely that all of these encounters are going to keep on happening until the human king gets wise and gives up. Or dies. Whichever happens first.
Then one market day you see Bolsaz Bloodaxe's delinquent progeny running past your stall after spotting the dread dark knight when the wind kicks up his cloak, realize that the little shit is going to tip someone off in exchange for some coin, and break off a sales pitch to lunge around your stall and catch him by the belt and send him sprawling into the road dust.
He's upset about it, of course, but you gifted his ma one of her best soup pots when she was still carrying him, and let his pa have your spare room for almost a year when he first arrived in Goblin Town without a red cent to his name, and even he's not enough of a discredit to his parents to raise a hand against you after you scold him for running so fast he must have caught himself on the corner of the stall, and it's just lucky he didn't break anything, because the sly gods know he can't afford it on top of those gambling debts.
By the time you've finished upbraiding him, and the attention on the (much more minor) spectacle has waned, the dread dark knight has left again.
...Huh. That gives you an idea.