In this particular case, there’s never a need for 16 bit math. The simplest algorithms for Conway’s Game of Life only compute one cell at a time, where you need to add neighboring cells - a value from 0 to 9 (if we include the central cell). As such, 8-bit math is perfect adequate.
On the VIC-20, I didn’t have that kind of memory, nor register width. So I had to do a lot of … weird stuff.
The bottom line, though, is that fast GoL algorithms on older computers is tricky to devise and hairy to debug. You can’t just look up fast GoL algorithms on the Internet, because they are designed for an extremely different regime. We’re talking massive tables and lots of frame skipping, because the goal is to search for various interesting things rather than to produce an interesting visual display. For a visual display, today’s computers are so fast that a dumb algorithm is adequate.
So, unless you really have to do something clever and time consuming to develop, just … don’t.
Anyway, 285000 additions per second is pretty impressive. The naive algorithm would dumbly do 16 adds per cell (8 adds to the array lookup; 8 adds of the values). Well, 285000/(72722) = 27 adds per cell. So, probably the simplest algorithm is being used. Much easier to debug.