ESL here, so I have to ask, does the title imply that this astronaut is a curious human as in he has a high degree of curiosity, or is he a curious (type of) human as in there's something curious about his physiology?
It could mean both, however the term is usually used when referring to someone’s personality, rather than physiology.
In this case, the article talks about his curiosity.
> One of the most curious humans
No doubt he is very curious, but there might be some selection bias here.