“Botched?” Not at all in the thinking of the time.
A short drop hanging was legal and would have been acceptable had the hangman so determined, and a long drop equally so. The belief that breaking the neck causes immediate death or even immediate unconsciousness is a myth that persists among many people to this day.
The doctors’ examination makes reference to death by “apoplexy”, an umbrella medical term of the day which corresponds to our modern idea of what happens to the brain when someone has a “stroke”. They thought he died mercifully in other words and that he lost consciousness quickly.
Some will say any execution which results in the death of the murderer is not botched. I agree with you that a hanging can be done badly and can be botched depending on the standard applied by the law and society.
The US Army’s 1947 “Procedure for Military Executions” includes a drop chart. You may find the manual interesting reading:
https://www.loc.gov/rr/frd/Military_Law/pdf/procedure_dec-1947.pdf
In the article
They mention it should have broken the neck but did not