Well...then they need to be okay with the chance that a guest *might* see them at some point during the day. Instead of putting up screens inside restaurant windows so guests can't see outside...on the off chance they may see some random person.
I think the screens inside restaurant windows may indeed be due to guests straining to see NBA players. My then 16 year old and her bestie would spend hours at a shopping mall hockey players frequent in the hopes of seeing their favorites. I could see fans spending the day at the window tables ordering ice water so they could get a glimpse of their personal favorite in the wild. By shielding the players from the public they no longer need to worry about the small crowds of gawkers blocking walkways or windows.