I'm not a scientist or philosopher, but here goes...
It depends on how to define 'sight' and 'seeing'. The human body is born with eyes, and the human brain is hard-wired to learn how to interpret the signals coming in through the eyes. It's a bit like the hard-wired ability to learn how to speak.
Light coming through the eyes is just an electro-magnetic stimulus. It is not 'seeing' or 'sight' until the brain interprets the signal, organizes it, and gives it a category or meeaning.
For someone who couldn't see, but then could, all other things being normal, it's just a matter of the brain learning to organize the light signals. Of course, if the person matured with no light signals coming in, it is very likely that their brain missed out on some aspects of 'seeing'development because of lack of input. Hope some of this makes sense haha! Cheers, interesting post.