Possibly bogus. Stupidly, I read the comments (when will I learn!) and here's a lovely selection/suggestion:
"Now I am doing much better in life and I tip very well when I get good service, if the service leaves much to be desired, so does the tip. I say to those in my party when I sit down, loud enough for the server to hear, "every time my glass is empty, I take $5 off the tip". and then I follow through. typically I get good service."
Greeeeeeaaaat idea. Passive-aggressively indirectly threatening your waitstaff, always a smart strategy to elicit good service. ;)
I think it's faked. The "single mom" handwriting doesn't match the other writing. There was a similar story a while back about a banker who supposedly left a 1% tip & wrote "get a job." It turned out to be an altered receipt. No mere 1% tip & no note.
What surprised me in reading the comments to the article you linked is how few posters even questioned the authenticity given the mismatched writing.
Link to the banker/1% tip story: