Sure, that's what I mean by an artefact of the filmmaking process. If we're trying to accurately figure out what the chase pattern was, that's useful to know - again, there is no indication that the LEDs are doing anything but a hard switch. This is one reason why they might appear not to be doing that, but I think they are.The shutter of a film camera is open for about 1/48th of a second (depending on the camera settings). If an LED is on for the entire period it'll appear full brightness. If it turns off before the shutter closes it'll appear dimmer. If one turns off and one turns on half way through the shutter open time, they'll both expose the film for half the time - hence you'll see 2 LEDs on at a reduced brightness.
Interestingly, if an object is in motion over a longer exposure period, it may not actually get any brighter - it may just produce a longer motion blur. People love to select the slowest possible shutter speed on video cameras (often 100% of the frame duration, so 1/24 of a second for movies) in the belief it'll make the image brighter. If they then shoot handheld, all it actually does is make the image smeary and equally dark.
We're now veering sharply into forensic motion picture examination, but there you go!