None of the boid AD modules that I found were what I was looking for, but in the process of looking through them and based on beachycove's comments, I came across something that was a similar animation. I think it was actually a swarm variant that I recall. There is a swarm AD module for 68K (the version that I found was 1.5 and it included the source code). Running it confirmed for me that it was not what I am looking for, but I am definitely getting closer. The screensaver was basically small rays of light drawn on a dark background and I know the one that I remember was dark figures drawn on a light background, with very similar behavior.
I think that I have a line on the buzzz module, so I will check that out and see what it contains as well.
The swarm 1.5 AD module runs fine on my LCIII, but I doubt that it will run on an SE (based on the documentation), so I think I'm looking for an early version of a swarm program, as opposed to a screensaver, but I'm willing to look at anything that might be close.
Thanks to all that have helped so far, I've come farther in the last week than I have in several years of looking.