It means nothing. Whoever writes this has no idea about American restaurant protocol. The "tip for good service" thing comes from the UK (perhaps elsewhere in Europe too, not sure since I don't know those cultures well). There (obviously it's changing as US cultural virus propagates) the idea was: default is no tip, a tip only exists as a token to denote thanks for something -- friendly service, quick service, and so on. Most service is slow and surly so -- no tips.

By contrast in the US the tip is mandatory. The server doesn't make any money and goes broke if you don't tip. So everyone does. Service would have to be astonishingly bad (waiter threw up on the customer?) to receive no tip. On the other end, one might give a somewhat higher tip if the server was particularly friendly, helpful, is related to you, is a friend of your kids, seems like they could use the money, and so on. There's no metric of "I was well served" that correlates to the tip.