somehow dragon can understand human and human can't
that is so weird, i though it's mutual (both doesnt understan). this reasoning would make more problem than not
My dog can understand a several dozen words. Hell, she can even lip read to an extent as well.She cannot speak them.
Dragons are not like my dog, but beings that are actually as intelligent as humans.
It's not really weird at all. It's no different from a mute person, who can hear and understand what others speak, without being able to speak back.
Another similar example is the series Reincarnated as a Dragons Egg, where MC(a dragon) could understand humans, but not speak to them until learning telepathy many evolutions later.
The only "weird" aspect is MC who is someone who magically can understand dragons(unclear how they communicate with each other). Which given it is a supernatural world, isn't a problem.