He wasn’t stealing; he was accepting a gift. If his customers had wanted to, they could have racked up those loyalty points themselves. They decided against it, and were probably in fact grateful that he was saving them the hassle.
Except that the terms of the loyalty card program probably said you had to buy stuff to receive the points. And probably said “not open to staff”. So he wasn’t stealing but he was probably in breach of contract.
I never give out my phone number when purchasing anything. I have yet to find a vendor that refuses to take my money when I make this stipulation.
Occasionally a cashier starts sputtering, “But we need it because…”
I just say, “No, you don’t.” Repeat as often as it takes.
Online, if it’s a required field, I put in a fake one.