The bill was $625. The restaurant charges an automatic 18% gratuity (about $112 in this case). Then Manning decided to leave an extra $200 on top of that. So a $312 tip. Which is about 50%. A 50% tip on a bill that large? Very classy thing to do.
Unfortunately for the waiter, he got fired after he posted the bill onto Twitter. The restaurant probably doesn't like the idea of people worrying about their tips (and the last 4 digits of their credit cards) potentially being posted online.