Fiora Q wrong target selection

I am flash Q'ing on Lucian here with 300 AD and a trinity force. My Q however hits Sion. As far as I am aware and according to the wiki since no vital was facing towards me and no one was in lethal range this should target the closest champion then - which would be Lucian here.

To avoid confusion: The dmg he takes after my Q is from auto that follows right after, but if you pause at the right time you can see my Q hitting Sion (also indicated by the grievous wounds applied to me via bramble vest).

I can't provide any information regarding the reproduction of this bug. All of this is assuming that I am not under a wrong assumption regarding the target selection. On r/Fioramains it was mentioned that the lowest hp target is focussed over the nearest, but that has never been my experience and I explicitly tested that on the PBE with the conclusion that this is not true unless the lower hp target is in lethal range.