I've never heard of that so-called Delhi incident.
It is possible that a pilot leaving his seat might, if very clumsy, have pressed the autopilot cut out switch on the control column. But that would have been obvious to the entire crew.
There were no overhead autopilot controls on the overhead panel, all were on the centre console.
It is highly unlikely that neither the co-pilot, air engineer nor navigator noticed that the autopilot had been disconnected.
The story sounds like total nonsense to me.