Jhin's Deadly Flourish animation begins at the widest (where it is equal to the effect area) then quickly contracts before firing.
In your image you just have the smaller portion just before it fires while clipping off the first portion (which would be all of .25 seconds earlier) where it is just as wide as the effect.
How it looks in its entirety: http://pa1.narvii.com/5989/6bdf4e3b3a924fcf8b26d9dddfd90f4864ea6dbf_hq.gif
To be fair, that's part of what makes it silly. Unless you have inhuman eyes and memory, the indicator isn't all that helpful. It should really just show where it's going to hit the entire time. A lot of the times, it doesn't even render on my screen at that wider portion and it's somewhere in that smaller one, or I'm just a scrub whos eyes need to git gud cuz I don't see it a lot.