There's no secrets at the 'Ring, it's monitored everyday by guys with cameras watching for exactly that.
Surely they didn't think a new run was going to be kept under wraps.
The guys with cameras rarely carry a stopwatch as there is no way to time a lap unless you have access to the start/finish lines - which they do not. Nor do they know which are factory cars making runs at the record, as most are practiced during "tourist" hours or club events. We suspect that one of the reasons there were "spy" photographers around this time because it was during the Frankfurt Auto Show - one of the largest in the world. Many of them were in Germany for the auto show and a few probably decided to wander over to Nürburg to check it out. Given that the Viper ACR held the top spot for almost three years, it would be a long time to camp out at the track hoping that you would see (but not time) another production car record attempt.
As mentioned previously there are live web cams at the track as it is, so knowing what is running is generally pretty easy. Getting the times down to the tenth (or 100th) of a second is something entirely different. No diss towards anybody - just pointing out how the track is set up.
VIPER magazine will have a nice article about how all that works, when and where the "spy" photographers hang out (same place anybody can on any given day), and how the laps are timed. No worries, the video(s) will come out long before that.
And Bob, getting everything synchronized is part of the process - lest all the geeks disassemble the video and proclaim it "bad" because the timer started a tenth of a second late or the lateral G's/downforce graphics were off from the actual direction of the car. Now a plain ol' video would be a piece of cake - and be dismissed by the critics in a matter of seconds. Your patience will be paid off soon...