From Wikipedia:
"Assange has not yet been formally charged with any offence;[35] the prosecutor said that, in accordance with the Swedish legal system, formal charges will be laid only after extradition and a second round of questioning. The High Court found that the Swedish process has reached the stage of criminal proceedings, which would be equivalent to having been charged under English process.[36]"
There is nothing preventing a Swedish court from issuing charges in absentia, and there's nothing preventing them from carrying out questioning outside of Sweden. This is smoke and mirrors.
And it's something that has prompted a formal complaint against this prosecutor to the Swedish judicial ombudsman.
They can still interview him without laying any formal charges. As far as I know the interviews are generally held long before the formal charges are laid.
From Wikipedia: "Assange has not yet been formally charged with any offence;[35] the prosecutor said that, in accordance with the Swedish legal system, formal charges will be laid only after extradition and a second round of questioning. The High Court found that the Swedish process has reached the stage of criminal proceedings, which would be equivalent to having been charged under English process.[36]"