different flexibility in different position

hy guys i want to explain you something that i see in my gym during a training...there a a guy who started the gymnastic activity and in the seated piked stretch he can touch he can grab his ankles and touch the knees with the chin...

BUT

if he tries to do the same from a standing position he seems to be blocked...his back is flat for 20-25 cm and he cannot make it curved...what can be? he can do very high kick (in martial arts) so i don't think is a legs problem...

do you have some tips?

I'd have to see more to attempt a detailed answer. But i can say that in some ways it is more difficult to get the chin to the legs in the standing version than in the sitting version. In part this is due to the fact a person has to balance making the last bit require more active compression than the seated version.

very interesting...so working on the active hips flexibility can improve this situation?