It's impossible to say anything with complete certainty without having a working sample of the camera to test, but here are some likely guesses.

First, there's no reason to assume anything about the shutter speed. The Sensor Flash uses a leaf shutter, so as long as the flash duration is shorter than 1/1000, the flash can sync with the shutter at any speed. That does not mean that the shutter is not set to a slower speed; just that there is no reason to assume that it is. You'd have to test to find out for sure by taking at least two flash pictures, one under relatively low light conditions for the film you're using (and with the subject about two-thirds of the max flash distance away for that film speed), and one under brighter "fill flash" conditions (but not so bright that the scene would overexpose at 1/1000 and f/2.8 without the flash). As often as not, simple cameras are either in "flash mode" or they're not, and when they're in flash mode they do what they can to get the ambient out of the equation. That would mean that the highest shutter speed that allows for the flash duration would be selected rather than the lowest.

As for the flash exposure, I don't see any signs of a flash receptor anywhere on any of the photos of the camera, such as one might find on an "auto thyristor" flash of the period. (There may be one under the flash lens beside the reflector bowl, but if it's there it's not visible in the pictures.) That points to the camera using a "flashmatic" scheme, where the aperture is coupled to the focus ring (in this case, electronically — on many rangefinders the aperture and focus rings would be mechanically locked together in this mode) to automatically set a nearly-correct exposure based on the guide number, film speed and subject distance. The furthest distance is based on the guide number and film speed at f/2.8; the closest distance is likely limited by the near-focus limit of the lens.

This, however, is mostly speculation based on what's available on the links you provided (and the links from those links). You ought to be able to confirm the behaviour with a single roll of film if you know what you're looking for, but I would expect a high(ish) shutter speed (underexposed ambient) and a "flashmatic" aperture selection.