That's kind of silly.
They probably suggested Chauboo since, well, it was the only Fighting type revealed thus far. And it was all the more relevant since it was in that issue. I'm sure had Aloe been, say, a Rock type gym leader, they would have shown off the other two as a suggestion. Plus, specifically showing a starter meshes well with the entire gimmick of Dento's gym.
I really don't get what you mean by being illogical game design wise.