This is true for Gnar's ultimate and Anivia's Q as well
More interestingly, these damages are also reduced by Randuin's Omen because they similarly count as critical strikes.
also;
GP barrels
Gragas barrels after 2 sec
MF Q on the second hit if it kills the first target
Sorakas Q if you hit it in the center
Vayne condemn, like Gnar "crits" on stun
these all count as "critical strikes" but aren't really