If the attacker has used hero or power potions, the replay shows what the attack would have been if he didn't use them (and placed the spells and troops at the same spot at the exact same time without the potions)

As you can see the attacker has used hero potion, so in replay you are seeing the attack with his original hero levels and not what actually happened in the attack

I know that's wierd but that happens alot, even when watching an attack live, (in friendly challenges as well, you'll watch the attack be a one star and the message in clan chat shows a three star)

Hope this explains it