Nautilus Passive Bugged? Staggering Blow Dealing True Damage

Just a bit ago I was in a match with Nautilus, and the post death screen kept saying his passive, staggering blow, proc was dealing true damage. I haven't tested this thoroughly to confirm yet, it could just be a GUI bug displaying the wrong damage type, but I asked other players and they say they are getting the same bug so there's at least something going on here. As far as I know, Nautilus, passive is supposed to proc physical damage.

Not really a game breaking bug since the passive in on such a hefty cooldown for most of the game, and its base damage isnt amazing anyway, but its still providing some unwarranted power to Nauts trading. Then again maybe its not so unwarranted? Having a true damage passive could give nautilus some much needed, reliable damage, reinforcing his role as a top laner without pushing his difficult to balance kit over the edge.