AIO gf told me not to thank a cashier because I shouldn’t talk unless necessary?

The context is that we were at a store, she was buying makeup. We went to the checkout, and a lady, maybe in her early to mid twenties was scanning her items. My gf says she was moody, but I didn't really see any moods in her the cashier was just doing her job and people in customer service have it rough anyway. She wasn't saying anything rude, she just wasn't saying much of anything at all.

After this cashier checks out our items, my gf says thank you to her and the girl says nothing back, then I say thank you and she says thank you back. Gf gets annoyed that this cashier girl didn't thank her, and only decided to thank me, and also mad at me for saying anything in the first place, because I should have seen her 'mood' and reacted appropriately.

We are both south Asian, but I've lived in the UK my whole life so I've always said thank you and am used to being extra polite to people because that's just how it is in the UK.

In the voice messages, she tells me 'not to talk unless necessary' and to 'behave'. Am I overreacting by thinking this is controlling behaviour?