But this dragon MC DOES have an "evil dragon" trait and "Path of Evil"/"Calamity" title, do he?

You can find it at Chapter 41 when he evolved into an Ouroboros.
Technically every one of us could become a victim of injustice and be officially judged and declared a murderer by the court, despite none of us, hopefully, having ever killed another person. But it happens and folks have rotted in jail for years for crimes they didn't perform. Are they evil, though? No, they might have never done anything fell so much they should be judged evil. Sure, some were guilty of many other crimes likely, but some were not and only had the one murder pinned on them.
Our dragon MC hasn't been doing evil thing. The hero has, most certainly, all the time. But then again, it seems to be a pretty shitty new world, so who knows. You might be entirely correct, with "good" and "evil" being totally arbitrary words over there. So, you might be evil even if you lived like a saint, sacrificing your whole life to help the poor, sick, and unlucky unselfishly. But if you specs say you are evil, you are evil.