Nope, zero hippos in the world of Nyx. So, internally, Nyx will just never know the joys of hippos.
The only reason, Nyx was so good with dogs, and other animals was simple. He treated them with immense respect. Always. Majority of animals were very intelligent creatures, and if you treated them respectfully and as if they weren't dumb animals, you would be surprised. So, he would befriend this dog, and it would be his buddy.
Just as he had done with Carbuncle.
There was another droll look from the Glaive. "What's a google?" There was so much he had to learn. The technology was so different. Shaking the mans hand, Nyx offered a smile. "Yes, nice to meet you also." Releasing the hand he looked about. "So what do you suggest I see or do here?"