In Sweden, two people can have consensual sex, during which time both parties consider it to be consensual, and then later, one of the parties can reconsider that view and accuse the other of rape.

That is what happened in the case of Assange. Who knows where Assange ranks when it comes to his level of compassion as a lover, but neither of the accusers claimed that he engaged in non-consensual sex with them. It happens that this after-the-fact rethink is called "rape" in Sweden. Most US publications published this detail in the fine print but proceeded with a character assassination campaign against Assange calling him an "accused rapist" without shedding light on the small detail that most people in the US consider rape to entail non-consensual sex.

Do you have a source for this (indeed peculiar) definition?

In France the information was that he had consensual sex first, then during the night he had sex without a condom unknowingly to her and/or when his partner was asleep (I cannot remember exactly) and it was this second case which he was accused of (which fits the description of rape)