They don’t know anything about those tickets, other than what’s written on them. What if the service was poor/slow? The food cold or bland? Flies flying around? The customer was elderly, and that’s the most they could afford? There’s a hundred reasons why the tip may be low. It’s a gratuity - to express gratitude or displeasure. If they don’t like how I tip, take tipping out of the equation and pay your servers. The dirty secret that most people don’t realize is that, in the US, if a servers’ tips don’t add up to the servers making at least minimum wage, the business is required by law to pay the difference. So this is basically a restaurant acting like a spoiled child - the customer didn’t give them enough, now we have to. WAHH WAHH!!
I would never again frequent a business that does this. You’re a business that relies on customer satisfaction, but you want to shame customers? Hard pass. I don’t care how good the food is. The other opt-out for me is any place that publicly says the tired, “Nobody wants to work anymore.” Lots of people want to work, just not for you, and you’re turning your poor business decisions into a political issue. Nope.