People are different. I can usually even answer a question on Slack without breaking concentration but if someone is talking to me everything's gone. Same as going to fetch a glass of water. In the office? Locking the computer and walking kinda far, maybe even locking/unlocking a door, meeting people? A real interruption. At home, 3m to the tap? Not losing a thought. But I do know other people who can talk between writing code and not be interrupted but if they have to answer on Slack they have the same problem.