Yes, the ocular scale proper is a transparent scale covering the eye, but a transparent scale shedding would still be, wait for it….transparent!
Actually, during the shedding the eye becomes cloudy. So, the snakes eye would cloud over, giving the appearance of one being closed. Another possible theory is that the snake inclined its head in a winking fashion. And the most probable theory is that JK didn’t put enough research into the ocular apparatus of boa constrictors.