Unfortunately, you can't really caution against people who are projecting onto a situation for whatever personal benefit / coping mechanisms they have. It sounds like you didn't do anything wrong in this situation, and that's the best you can do. It's unfortunate too that people are uncomfortable to ask questions, and just assuming things they hear about someone are true, especially when it's in a bad light, ask to confirm or hear the 'other' side of the story - and gauge for themselves believability of both parties.