That doesn't tell us it was targeted - perhaps that's not the explicit claim the article makes, but it is certainly implied. If Facebook can't control the impressions for each ad partner, it's likely more than just Mother Jones were affected. If their algorithms are bad enough, driving people off the platform, that might also contribute to declines. (This is one major reason I no longer use FB: it can no longer serve any of the baseline purposes it was intended for, because of how poorly its feed algorithms work.)