Im not the guy you quoted but I can absolutely state I believe its a mistake.
The mounted guard arent just riding a tiny horse like reva is. They're tiny people on tiny horses. I took a picture of them next to sidir and a guild riflemen which someone posted to the guild scale thread as well; Sidir and the riflemen are taller than the guard and their horses together! There's no fluff for that.
That being said, they're beautiful models and beautiful sculpts; they just look stupid next to anything else.