All of the trophies currently in existence for FFxiv were implemented at the same time when the game was crossed over to console platforms. As such, all of those trophies are only relevant to that content. That means that the "Slay Thy Neighbor" trophy is for Wolves Den (now "The Fold"), because it was the only PvP available at the time. Front Lines was not implemented until 2.3 (Defenders of Eorzea), so it doesn't count. At the time, the wording of the trophy was accurate; however, it really should have been adjusted after FL was introduced.

Regardless, All of the trophies relate to only the content that was available at the time (for example, you'll also notice that the only raiding trophies are for The Binding Coil of Bahamut, which includes only T1 through T5). None of the wordings or conditions of any of those trophies have been adjusted since they were implemented, nor have any new trophies been included for any of the new content, including expansion content ... which kind of sucks, since it gives additional incentives to do certain content.