Mirror Matching

The answer is likely mods (though strategy can also come into play).

Power is a meaningless stat. Stop thinking of it as something that may determine victory. There are so many ways this could happen with the limited information you gave. But again, one of the likely explanations is they were modded better than yours. Relic levels aren't everything either.

Various factors can affect the outcome but Padme mirror matches in general are a courage-stack rollercoaster.

I would say if their Anakin has high courage stack count when you kill their GK, he takes his turn with an AOE and can wreck your team.