Levellass basically answered this already, but maybe I can make it clear:
Most mods have 1 for 1 enemy replacements. This is basically the easy way to mod a creature and was the normal, hence why mod wiki pages would point out that replaces what.
Technically creatures and other sprites don't have to be done that way. You don't have to have 1 for 1 replacements. The Krodacian Drone is a case of this.
The reason the Krodacian Drone its listed as replacing a goplat is because it uses a goplat spawning sprite from the original Keen 5. I'm not sure it would be technically correct to say a goplat was patched into the enemy but thats the general idea.