Perhaps the fact that they share the same fur and color patterns make it incredibly easy for the two of them to get along well. When they first saw each other, they assumed they were meeting their siblings, but the difference in their mannerisms allowed them to quickly decipher that they were two completely different creatures. But when has that deterred them from getting along?
They ooze out empathy for each other and always protect each other's blind spots. This particular dog is eyeing up any incoming predators, scanning them for potential weapons and can instantly lunge at them in self defense should it come to that. Meanwhile the cat has completely curled up on top of its canine pal's warm, fur which has the same color schematic as its own body.