Upon taming a horse for the first time, two in-game days into a completely new Survival world (no cheats or starting chest activated), I got the '[A Complete Catalogue]' Achievement, even though I hadn't tamed any cats prior to taming the horse.

What I expected to happen was...:
I get just the '[Best Friends Forever]' achievement, and tame the horse.

What actually happened was...:
I got both the '[Best Friends Forever]' achievement AND the '[A Complete Catalogue]' achievement, on top of taming the horse.

Steps to Reproduce:
1. Find a horse.
2. Right-click horse until tamed. (Do not use any wheat, apples, etc to speed up the process.)
3. Get both mentioned achievements.

(Screenshot attached.)