Your edit was indeed helpful. Your changes were absolutely improving the answer and, as you said, it wouldn't even run without the missing quote. Most importantly, you fixed the (( failed )) || return which had to be (( failed )) && return for the script to work.
When looking over your edit, I was confused by your change of
if ! "$*"
I agree that the first version of the answer was severely flawed
— I’m the one who down voted.
I agree that it’s OK for edits to fix technical errors in answers.
Reviewers often reject such edits
with the “clearly conflicts with author's intent” reason.
It seems to me that this argument says that the author intended to post
a technically flawed answer, ...