If anything at most he is a half breed, I don't see him as being a dragon descendant completely. There are things that wouldn't make sense otherwise. He should be able to have wings by now at the very least or other kinds of powers considering rose already does.
My thoughts were that he was secretly a halfbreed from the get go but they still haven't told us enough about his parents or past. I think they aren't his original parents anyway and they either found him or were asked to take care of him by a biological parent during one of their adventures for relics but this is still a longshot guess.
I seem to refuse to believe that he is just an ordinary human and those are his real parents. Being a "level 10 breaker" isn't enough focus cause there are other level 10 breakers in the story apparently and that would make him not special in some way. Anime stories always have something special about the main character
"The people cannot be [...] always, well informed. The part which is wrong will be discontented, in proportion to [...] the facts they misconceive. If they remain quiet under such misconceptions, it is lethargy, the forerunner of death to public liberty. What country can preserve its liberties, if it's rulers are not warned [...] that this people preserve the spirit of resistance? The tree of liberty must be refreshed from time to time, with the blood of patriots and tyrants."-Thomas Jefferson