Hi Stefan,
thank you for the pics.
Well, but should not uncareful folding also cause scratches in direction of the moving bottom tube - in riding direction?
Doesn’t it look more like signs of pressure force across the driving direction, applied at the folded bike?
If you lay the bike either on its left or right side - are there any (pressure) marks?
Did you try to look along the center axis of the tube(s) - are they bent?
May I suggest you show the frame to your dealer AND a second, independent and renowned bike mechanic?
You’re right, low pressure and Kojak does not match 
…and, funny thing that you mention these tyres, some time ago I was searching for them without success
MAXXIS Hookworm 16" x 1,95 (53 - 305) tyre request
but, last Thursday I’ve got a pair Hookworms from Chainreaction cycles
(Have to swap the wheel set first, both of our Stridas here are 18" wheeled at the moment.)
Did you notice the small modification which is required for wide tyres and proper magnet function?
Sorry, but I’ve never tried to fix a Brooks saddle on a Strida…or even had a Brooks in hands 
Cheers,
C.