What Caused This iMac to Suddenly Start Smoking?S

A reporter at Chinese tech news site, cnBeta, says he was just chatting away when white smoke started coming out from behind his iMac, turning black just as he cut the power. Here's the video he captured with his iPhone:

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Yeah we've heard stories of exploding iPods (like this UK girl's) but I'm not saying this is part of some trend or anything. I just wanna know what you think happened here.

Looks to be enough air flow there...it's just gotta be one of those rare screen failures, right? You tell me. [cnbeta (translated) via Cloned In China]