Assalamu Alaykum,
Usually people who are intelligent make sound decisions and follow the truth. How come people like the chinese are technologically advanced and at the same time either buddhist or atheist?. Can you provide an explanation from the Quran and sunnah?
Thank you

All perfect praise be to Allaah, The Lord of the Worlds. I testify that there is none worthy of worship except Allaah, and that Muhammad is His slave and Messenger.

What you mentioned in the question is correct and this proves a very important matter which is that it is Allaah Alone who enable people to be guided. No one can be guided or guide anyone else by his own will. Allaah Says (what means): {Indeed, [O Muhammad], you do not guide whom you like, but Allaah guides whom He wills.} [Quran 28:56]

On the one hand, a person may not make proper use of the means which Allaah blessed him with, like the sense of hearing, seeing and reasoning, and he does not use these senses in order to arrive to the truth. Allaah Says (what means): {And We have certainly created for Hell many of the jinn and mankind. They have hearts with which they do not understand, they have eyes with which they do not see, and they have ears with which they do not hear. Those are like livestock; rather, they are more astray. It is they who are the heedless.} [Quran 7:179]

On the other hand, the truth may be manifest to a person but some matters may prevent him from following it, like being proud of what the fathers and forefathers were upon, or due to being overwhelmed by desires, and other reason of misguidance of the people. Allaah Says (what means): {They are not but [mere] names you have named them — you and your forefathers — for which Allaah has sent down no authority. They follow not except assumption and what [their] souls desire, and there has already come to them from their Lord guidance.} [Quran 53:23]

Allaah Says (what means): {And when it is said to them, “Follow what Allaah has revealed,” they say, “Rather, we will follow that upon which we found our fathers.”} [Quran 31:21]

Allaah Knows best.