New player, a few weeks into actually playing myself, but with friends that are more heavily invested that taught me.

By all sources I can find, Hexproof blocks spells and abilities that specifically use the word "Target" when referring to a creature. However, in MTGA I am able to use Act of Treason (which specifies "target creature") on Hexproof creatures. It was an accidental cast the first time, and then after that I did it intentionally to test, and sure enough it ignores Hexproof. Is this a bug, or is there something I'm not understanding about either Hexproof or Act of Treason?

Edit: It was against a Carnage Tyrant, controlled by my opponent. Only cards in play by me were a Ghitu Lavarunner and a Viashino Pyromancer.