If you were the owner and the guy had just trashed your pool hall on social media how would you handle it? Would you say anything to the customer? What would you say to your employee?
Id like to think I'd let customer know his freebie that used cleaned balls as cb had some negative impact, and I'd acknowledge the opportunity was provided by my employee.
I'd let employee know her failure to pick up after herself created a potential conflict.
But as I said...it is really a minor thing.