It could be that even if it doesn't seem like that to you, it sounds like that to them. Surely almost everyone has gone through lots of experiences where they interpret someone correctly to have said something offensive, at which point the offender attempts to weasel out of it; perhaps that's the template you're matching in their mind, even if it's not what you're doing. By comparison, the number of interactions where someone is trying to explain a difficult concept is pretty small, outside of certain small groups.