This is the first time I've seen this particular photo, thanks for sharing. It is nice and sharp, and really interesting to look at. The tyres are surprisingly thin.
There is a nice line-up of proto-PTs to be found on the following page:
https://msu.edu/~luckie/segway/idea/idea.html
The C1 shown in this line-up is photographed from a front-side aspect. It has had the spokes of the wheels milled out (unlike the solid wheels in the Concord Monitor photo). The two other things I noticed are the use of 3 wheel nuts (Gen 1 uses a single nut, Gen 2/SE use 3 nuts), and it appears there was no built-in charger on the C1 (which left lots of room for feet, and no doubt lightened overall weight).
Philip