To be honest, I’m not 100% sure this is a bug, the highest title for sPvP achievements is the same as getting 25 points in the Hall of Monuments, they both reward the “Ascendant” title, and no other 2 achievements reward the same title (especially for such different tasks).
Seems odd to me, so I figured its probably a typo or small error, was hoping maybe for ANet confirmation on this.