Skill description semantics
Have you never heard of someone “running away in fear”?
Startle would be closer to what a stun does, where they are so shocked they just sort of sit there for a moment
That’s the point. A thief is able to land 3 heartseekers on me while I run away like a headless chicken. In turn, when I fear a thief, he turns around, starts running then changes his mind, turns around and proceeds to send me into downed state.
Well, unless you really put some effort to making your fears last longer, it’s more like shouting “look out, there’s a thief behind you!” which might be enough to make the opponent turn their head to the other direction and on the occasion even move that way before reconsidering. Sounds more like something a mesmer would do though.
Always remember the Rule of Cool (http://tvtropes.org/pmwiki/pmwiki.php/Main/RuleOfCool) too. Instilling Fear in enemies sounds better than to say that you Startled your opponent.
Plus what others have said, people run in fear. While they stand or jump in startlement, they don’t flee in terror.