This is a philosophical one, so apologies if it's not appropriate. I can think of several reasons that Conway's Game of Life would be rediscovered by any mathematically inclined biological life forms. The strong visual language of GOL would also make it especially appropriate for interspecies communication.
- 2D cellular autonoma on a square tiling of the plane are likely to be explored because 2D environments are of particular interest to three-dimensional biological organisms, since they perceive the world as 2D projections. Square tilings are going to be explored because it's one of the few ways to regularly tile the plane. Cellular autonomy are likely to be explored because of the analogies to biological life, and it's a tantalizing use of computation.
- As far as I'm aware, Conway's game of Life is by far the most interesting of the simple neighborhood CA rules. The diversity and complexity means it's likely to be explored in depth, not to mention that it is Turing complete, something again of interest any technological species that has studied computation.
Are these assumptions legitimate or am I being ethno(?)centric? Is it reasonable to think that images of a glider, a small spaceship, and, say, the acorn methuselah would be recognized universally by any technological species?
Well yes, you are certainly being ethnocentric, because none of us can help but to be. Your arguments sound plausible to me: I find it hard to imagine a technological species which didn't have research in maths and science similar to ours. But of course that's almost certainly a failure in my imagination rather than a significant observation. I guess that any species sufficiently advanced to (say) communicate with Earth would have to have algebra, calculus and Newtonian gravity, essentially in our form. Maybe that applies to GOL too. It would be wonderful to know more but generalising from one case to the whole universe is probably pretty risky.