IQ isn't static, so it's quite possible for someone's IQ to dip out of the "genius" range. Interpreting Reiser's increasingly bizarre behavior as signs of internal dysfunction, it's quite possible he would no longer test as a genius. Certainly, turning down a 3-year plea offer and insisting on acting as his own counsel would be indications to this layman of sub-genius performance.

Since we're talking about a headline instead of a clinical diagnosis however, I'd suggest the author was using that phrasing as a more concise way of communicating "formerly known as a software genius, then famous as a convicted murderer, and now working on a shtick as a mad scientist."