My Exposure Race Maxx has two side by side LEDs in it, but confusing the 2cm or so separation of that with the 1.5m separation of a pair of car headlights would take some effort.
Similarly, my bar end lights are normally in a flashing mode (to keep the battery life sane), and are used in conjunction with lights on my carrier / seat pin, so it would take a lot to confuse three lights (some flashing) with the rear of another vehicle.
There is some possibility of confusion caused by light dimensions, but the only time I've ever experienced it, was with a relatively old mini. Since it's headlights had a relatively narrow spacing, and were dimmer than most modern cars, for a brief period I thought that it was further away than expected, however once it did start to approach me, I realised what it was due to other visual cues and the variation in the speed of change of the original visual identification items. This also only really occurred since the spacing and brightness were close, but not quite what I expected, not the vastly different variations that we are talking about.
Recognising a vehicle, and it's position and speed is a complex matter, you don't do it based on lamp spacing alone, even when quickly glancing at the road. Light intensity, and position compared to other cues will also be important. Most of us are rarely on a totally dark road, and utterly isolated compared to other light sources. One of the few places that this can regularly occur is on a motorway, where the lack of road lighting, and clear view over substantial distances, can often mean you see other vehicles purely based on their rear lights. This isn't likely to be an issue with pedal cycles!
I think that for cyclists this is a non-issue. I've never looked, seen a bike with two adjacent bright rear LEDs and thought that it was a car several miles away.
