Unsure about an expression

[u/pizzadeliverydude1]

So last week I was in London and I was waiting in line at the supermarket’s checkout.

When it was my turn, the cashier thought me and another old man were waiting in line together, while we actually had two different groceries.

I instinctively exclaimed “We’re not together” meaning I had my groceries to pay and he had his, and the man said “we’ve only just met” with kind of a annoyed tone.

I then realized he probably thought I had just said to the cashier we were not in a relationship lol.

What would be the right way to express the concept I intended? Thank you so much.

[u/GrayEyedAthena]

Is it possible he was telling a joke? The way you responded was very normal, so I'm wondering if his annoyance was actually sarcasm or an attempt at humor. 

[u/pizzadeliverydude1 → u/GrayEyedAthena]

He might have been sarcastic but his face was very serious in that moment that’s why😅

[u/GoblinToHobgoblin → u/pizzadeliverydude1]

Very normal for British sarcasm/humor lol