a way to increase true damage?

So, i was playing mid morgana earlier and i forgot to swap from smite from the last game as jg. Thought to myself, "well at least i won't miss any cannons." so after a while, i realized something... my smite at some point had started doing more damage to cannons than the number stated in my buff bar. at first i thought it was some sort of bug, right, but then i realized something. I'd used my minion dematerializers up. and apparently, they also increase true damage. Loaded up the practice tool after the game and got on master yi and used wuju style to see if it effected that too, and it does. Minion dematerializer increases true damage. Was curious if this was intended or not? I was under the assumption that true damage was not intended to be either reduced or increased by any means.