In this case, its a newspaper article that are citing Assange, which is why the sentence beginning with "Julian Assange said". Changing it to "Julian Assange allegedly claim" would make the article worse, as the implied disbelief of using the word "allegedly" is not supported by the source.
Having to base edits around sources is hard, but I think a crucial aspect of any encyclopedia. The alternative is just so much worse, don't you agree?