Immortal ranged minion with 0HP.

So we played a custom 4v4 draft game on aram. Vel'koz, Veigar, Azir, Yorcik VS Xerath, Vladimir, Xin Zhao, Yasuo

And then I suddenly found this little guy. A ranged minion, immobile and totally pacified (like if it was stunned or something). It also had 0 health (as the image shows) and it had no unit collision (even my Vel'koz Q vent through it). I guess it was a minion that got killed but stayed visible or something similar.