I definitely was on the IC, it was
non-stop between Bern and Zurich. Using Zurich HB as a point of comparison, it has sectors A, B, C and D while Bern has only A, B and C, the sector lengths in Bern
should be longer than in Zurich.
The platforms in Bern have a sector D too, at least those that are 400m.
I still think that you boarded the added module, and not the main consist. If the train was indeed as short as you describe you would not have been able to get on.