To be able to choose wisely, one has to be of a certain age - usually at least later primary school. For piano, that will be a little too late - if the child is to complete the exams. Once the child leave secondary school, music exams will be an added stress. So if he does not complete his exams by secondary school, it is likely that he will not complete it.
So at a young age, parents have to make a choice for the child. Same with everything - we choose the clothes they wear, we choose the food they eat, we choose the books they read, we choose the TV programs they watch etc. Until a certain age, they will be able to choose themselves.
I don't see choosing for the child as something wrong. It is in fact necessary. But I don't agree with forcing the child - that is the method to encourage him. It is OK to pick an instrument for him at a young age - then if he later feels he doesn't like it (at an age when he can make decisions), we can help him see the various options and guide him along.
It all depends what you want the kid to do. Music can be just a hobby. But it can be a career. As we all know, the best career is the one you enjoy. If he enjoys music and can make it a career, then it is the parent's responsibility to help him achieve it - at least provide him an option to be able to achieve it if he should choose it eventually. And if he loves music and wants it to be his career, he should be good at it - not just mediocre.
Although my parents did not force me, they did "strongly encourage" me - perhaps a little too strong. But they did choose my first instrument. They were not rich; we lived in a rented house then. I'm grateful to them for that - because they provided me the opportunity to choose later in life. I was able to choose music as my career if I wanted to. But of course, I didn't. Still, music played an important part of my life. But thanks to them, I am able to play 4 instruments and compose music today.