I'm pretty sure it was a track day, rather than touristfahren, which would explain
a) the cars parked up together at the start
b) the lack of bikes (track days there are normally cars or bikes)
the overtakes would look exactly like that as people aren't racing. once someone's caught you on a track day, if they're going quicker than you, you get to a place you can ease off, and let them past (on the left, if its a touristfahren).
The overtakes might have been scripted/repeated, but they're not contrived. Sabine in a car like that would probably be quicker than any member of this forum, in literally any car. Just in the same way that Danny hart would be quicker than any of us down fort bill, regardless of the bike he's riding - particularly if (as the analogy would follow) he's just on a mid-spec enduro bike (so pretty reasonable, if not absolutely optimized for the track) rather than a £10k carbon bling spec dh bike (ie a 911 gt3 or turbo)