According to the article:
"Many of the charges against those executed are recorded as blasphemy and spying, but others include sorcery, sodomy, practicing as a Shia Muslim," the report states.
That is indirectly saying that Shiites living in ISIS controlled territory should convert to Sunni Islam, if they want to live. Earlier, the Christians were also given three choices: pay jizya, convert to Sunni Islam or face death. In case of the Shiites, the first option can't be used, as they are also fellow Muslims. So there are only two choices.