There were multiple sources quoted for the Al-Jazeera article detailing Iranian president Mahmoud Ahmadinejad's uranium boosting proposal to Iran's Atomic Energy organization.
First off, Ahmadinejad's televised statement provides the primary source for the article. His announcement came as a surprise for Western powers of the world especially after the P5+1 and the IAEA proposed an agreement for Iran to ease back on their nuclear fuel production and not invest more time exploring the powers of uranium.
Secondly, having quotes from said Western powers like Robert Gates and John Kerry gives good perspective on the dangers of such a proposal Ahmadinejad's making. Their quotes express the concerns of the Western people well.
To counter those statements, Al Jazeera offers up Tehran University professors' viewpoints on the issue, stating that countries like the U.S. like to peg Iran as the bad guys in this situation and they go on to give their opinions on the issue.
The quotations are spread throughout the article but appear at the right point in the story. For instance, you don't read a quote from an Iranian professor right before you read what our Secretary of Defense has to say on the topic.
The information used in this article isn't public record but it was publicly available on state television in Iran and online (I searched for the P5+1/IAEA agreement presented to Iran and found what they had written up here). I assume Iran's written rebuttal to this proposal will become publicly available once it is presented Monday.
The attributions for quotes are set up with the partial quote format of "Statement, statement, statement," he said. "More statement." I wouldn't say this is confusing at all. It's effective in that each person quoted is provided more or less the same "newshole" to get their opinions expressed. Very fair reporting done by Al-Jazeera, I have to say.