It doesn’t even need to be a stream sniper; If a player has played against the opposing team multiple times in a row and knows their favored heroes (not to mention, if the player is very experienced with thousands of HotS games under his/her belt)
they can predict the full enemy draft in advance or very close to it.
I can remember plenty of usernames and their favored picks. If I see multiple of these players in the same lobby on enemy team, I can predict 2-3 early picks with ~90% accuracy.