Should she have said that I stole the drink?

Solution 1:

If the barista was a non-native speaker, they might have used *“He steal(s) yours” because they didn’t know a better word. But this expression is also used by native speakers.

“He stole your drink” sounds like a joke or exaggeration, probably to put the other customer at ease. In casual speech, some people use “steal” as a joking way of saying “take”, especially when said with a positive/light tone. It doesn’t imply any malice or wrongdoing like “theft” or “robbery”. For example:

[Alice and Bob are at a restaurant.]

Bob [buying a burger and fries]: “Do you want anything?”

Alice: “Nah. Mind if I just steal some of your fries?”

Bob: “Sure, no problem. I’ll get a large.”

(This is a playful way for Alice to ask Bob if he will share his fries instead of buying two orders.)

In the situation you describe, you could have made a similar joke, like “Oh! Sorry, I accidentally stole yours.” In that case, it would be a mild form of self-deprecating humour.

Solution 2:

It's perfectly idiomatic if what she said was "someone stole yours". As tchrist says, the present tense would not be right here.

The verb "steal" is used all the time jokingly or in a mildly annoyed way to describe situations where someone accidentally walks off with something of yours, especially something of little value. It's also used with things that aren't really possessions, like parking spots.

I'm a native speaker and I would probably joke around with my friends saying that they "stole" something, usually with a tone mocking seriousness so that it's obvious I'm joking. What was the tone like when the staff said it? Given the circumstances, I can only imagine it was a joke.

This same thing can be seen in writing, notably memes:

(Click on any of the above images to be taken to its source.)

Now, all these memes are jokes. The first image probably illustrates how lightly we use "steal" best of all, since the mom whose spot was stolen isn't accusing her newborn of petty larceny, yet still she says that the baby stole her spot.

There are, of course, other ways to say it, but that's another question.

Solution 3:

If this was a busy, noisy place, then it's possible that you misheard what was said. This is more likely if the speaker's accent is different to what you are used to hearing, or they are speaking quickly, or their pronunciation is sloppy.

It would be extraordinarily thoughtless and impolite to say that a customer was stealing from someone else in a shop.