They just grabbed the wrong cup and ran with it. Please don’t think too much into that.

This used to be part of Starbucks' ploy to keep customers coming back. It was called "surprise and delight" so we were encouraged to occasionally spontaneously upsize customers, give away mistake drinks, etc. and a long time ago we could even treat customers to free drinks.

This isn't something that happens much now, I don't believe it has been in years. Most likely the barista either grabbed the wrong cup, or they made too much and just upsized you. Or if your drink was a generic drink, you may have grabbed somebody else's order.

Definitely don't read too much into it. It makes it awkward for you and the employee.

Tbh we don’t haha

I wrote my number on someone’s cup my first month and never got a text or anything 😔

So I never did that again

Looking back at it, it is sorta creepy