Opponent bought a victory card triggering the two black cats in my hand.
They caused me to draw more black cats which were also triggered by the victory card purchase? I wound up playing like 6 or 7 black cats in total.
Yes, that is not a bug but correct behavior. Since nobody except you can know if you actually drew the Black Cats now or if you had them in hand all the time, the game allows this to happen.
Not skewed at all.