According to this article
Bell, seen above, said her notation on the receipt was a “lapse in judgment that has been blown out of proportion.” Despite scratching out the tip added to the bill, Bell claimed that she left a $6 tip in cash, adding that she subsequently discovered the 18 percent gratuity had been charged to her credit card.
In addition, I'd be willing to bet that what the pastor saw on her credit card was the authorization which would have been for the full amount. Many people don't understand when they see a 'pending' charge that it's not the final billing, it's just what was pre-authorized (which we saw was done from the pictured receipt).
As for the public outrage, there's a saying, "Hell hath no fury like the uninvolved." that applies here nicely.