Knowing someone has made a specific choice can only come after it's been made, yes. That's a matter of physics although those espousing gods and the supernatural often make claim to knowing the future in advance. One certainly can say if accepting the theist claim to 'free will'. The reality would be that they can either freely choose to eat the fruit or freely choose not to. A claim that their free choice requires an external determinant, (the snake), is to deny the very free will it demands exists.