I considered the drifting horseshoe as well, but I thought if you were looking out from it across the track you would see the concrete viewing terraces behind the retaining wall. The terraces are not visible in the photo above. But, I am not really sure.
Edit: The concrete terraces were added at some time this decade. Turns 10a and 10b were drastically reprofiled a few years ago. The drift horseshoe was added in the last couple of years. The photo could have been taken before that. That right angle road could be the service access road at 10a. Obviously, I am still confused.
By the way, when we go to the Petit we usually view from the top of the concrete terraces. The viewing is better from the other side of the track (inside the track), but that viewing area is prime and you have to get there pretty early to grab a spot. As party crowds continue to increase at these big events like the Daytona 24, Sebring 12, and Road Atlanta Petit we've decided not to fight the masses if it can be avoided. Gotta find a middle ground where the event is still enjoyable and worth attending.