First of all, the way you formulate your question is fallacious, but that can be not on purpose so i'l just go over it.
The (not "my" like you said, but "the") common definition of honor is : high respect or great esteem toward something, that can be toward morale, but not necessarily, in this case for example, its toward duty.
2nd like i already said, he eat peoples, livings beings that not his kind, like those peoples do when they eat other livings beings that not their kind, this point is not about murder or balance of power, he just eat animals, if a cow was better to recover his power he would eat cows and not humans, so taking it in the honor thing is just hypocrite.
And finally since he isn't suicidal, he know those "stronger than him" who chased him would kill him on sight so he couldn't talk to them even if he wanted, therefore he couldn't known if they did it by duty or not (spoiler : no), plus the fact that until then he already have contact with other superhumans and none of them have been honourable.
But he speak with the MC and he acknowledge the MC is not fighting him by thirst of power or knowledge like the previous ones, but by duty toward the title that peoples give to him (hero) even if he didn't claim it himself, and its cause he showed respect toward that that he changed the place of the fight, allowing the remaining humans to live, giving respect to the MC duty by that, despite his own interest.
So at the beginning of the fight, only Valravn show honor, the MC show it only if he fight until the end without help, cause he asked for a one vs one that not involve humans in name of the duty of protecting those humans, in the line of choices when you win thanx Brianna you break your words, by involving those you were supposed to protect for win, making this win dishonourable.
After we can think honor is superfluous, not important, less important than win or whatever else, that up to each one and it another debate, but fact is : Valravn shown honor in this fight, and if we win thanx Brianna we didn't, we can also notice that in the dead event he still speak to the MC with respect cause in the dead event we didn't involve anyone, fighting with honor until the end.