Ok so I was playing against the AI (Star Realms Android app) today and every time I played a card that should have had my opponent discarding ( Imperial Fighter), it instead made ME discard as I played the card. In addition, the AI still drew 5 cards at the start of their turn. This has to be a bug, right?
The campaign game changes some of the rules, depending on which mission you are playing.
For example, on Mission 3 "A test of strength (hard)", the rules are
[...] If you would make your opponent discard a card, you gain 2 Authority instead. [...]
I'm pretty sure you were playing a mission with special rules.