I could actually observe his surprise & confusion at what was happening, and his inability to resolve the solution (simply turning the heading back to original intercept).
The solution is easily resolved by following the advice recommended in the Children of the Magenta Line video.
And that is "CLICK CLICK" disengage the autopilot and if appropriate the autothrottle, and without delay manually recover the situation to get back to the desired heading/course/whatever. Whatever actions take place after that depends on pilot discretion.