I first learned of Vinge's Singularity concept in his novel Marooned in
Realtime. This novel deals with survivors who were in stasis and missed
the Singularity, which left the world mysteriously absent of human life.
>From the information in the novel given by the character who lived closest
to the Singularity, it does not appear to have been caused by advanced AI.
Instead, it is a matter of technology allowing for telepathy-like powers
which create a group mind. It appears that Earth was on its way to
binding everyone together into a super-intelligence which would have
powers far beyond the individuals involved.
I don't know if Vinge advances this hypothesis seriously in his nonfiction
writings but it does appear that he originally conceived of a Singularity
through other paths than AI.