That isn't exactly correct as it is more of a quick stop for a bite and drink certainly not just coffee and tea. We of course don't know what the original Italian said so they may have translated the word for bar (non-Italian meaning) correctly.
It is possible C&S saw them there before the testimony started and if legal in Italy it is unlikely they would have filed charges.
An ex parte meeting seems wrong to me regardless of time of day until after testimony is complete.
Google is a wonderful tool isn't it? Ever been to Italy? Can you not get food and other drinks at a coffee shop? Typically they're tiny and Italians don't sit down for their coffee. They stand at the bar and have their espresso/cappuccino. They very well could have randomly encountered each other there.