I am just going to guess this one as I don’t have either heroes. But here’s a possibility based on my experience with other heroes.
In case of hero specials, all the effects are applied in the order in which it is written on the card. So first he applied sand damage, which gets reflected back to his team. Then he applies -50% healing which also gets reflected back to his own team. Then he cleanses all his teammates. Since the healing debuff is undispellable it stays, but the sand damage is cleansed.