The achievements track progress across all characters, not a specific character. World explorer (Been there, Done that!) is character specific.
Check each zone (Metrica Province, Queensdale, Straits of Devastation, etc) to make sure each zone is 100% complete. Also, make sure that all towns (Divinity’s Reach, Lion’s Arch) are 100% complete. I believe WvW 100% complete (four maps – all three borderlands and the eternal battlegrounds) must be completed to receive full world explorer.