[mnehring]

....and then observed this second object - moving at between two and-a-half and three times the speed of the space station.

Speed is something they can't determine unless they also knew the distance. If it where an aircraft flying in between the space station and themselves, it may appear to be going faster when in fact, it could have been moving slowly relative to the space station.

[DBrow]

If you substiture “angular speed” it makes more sense.

With angular spped, my fingertip can move hundreds of times faster than ISS!