About two weeks ago my sister had a friend over at our house. It was a slunný day, so they spent afternoon in our garden with pool. The friend lives in a flat. I came to greet her but then I kinda stayed. She had her one year old son with her and she is interesting person to talk with. I spent my days at work where you can't interact with people in any meaningful way. Everyone seemed to be ok with the fact that I was in the garden with them. Yesterday, my whole family went shopping, we argued about something, and suddenly my sister mentioned that she hated the fact I was there when she had a friend over, and that she thought I would just say hello and leave them. She was apparently angry at me, but didn't say it at time because she said she didn't know how. So am I the asshole in this situation?