Lol, I used to work at Starbucks and Customers could put it in the basket or hand it over to you personally. Not knowing any better, I would put it in the basket, but eventually the customers would insist that it was only for me or just hand over it while I was mixing their drinks. One of my managers would get heated, but the one of the customers straight up told her, "bytch, if I wanted to tip everyone I'd put it in the bin. I only like his service, don't make me call HR on this whole store" and she stepped back.
That customer needs to come in and call out the manager. That's just bullshyt. I understand the kitchen gets tips, but they clearly only wanted her to get it. You can't just make up some policy when someone drops 4g.