In some countries it's not considered a slur. In the UK, the government's list of ethnic groups contains 'Gypsy or Irish Traveller' - https://www.ethnicity-facts-figures.service.gov.uk/style-gui....
But in fact it seems to be the term used by some Romani groups
> The term Gypsy, which originates in the word "Egypt", mistakenly believed to be the original homeland of the Gypsies, has been controversial.[8] Some Romani activists reject the term, but it is embraced by others.[8] Although the term "Roma" was endorsed in place of "Gypsies" at the first World Roma Congress in London,[9] many Romani people in Britain prefer to call themselves Gypsies, or names that include the term such as Romani Gypsies or Romany Gypsies.[10][11][5][12][8][13] They also commonly refer to themselves as Romani or Romanies.[14]
(from https://en.wikipedia.org/wiki/Gypsy,_Roma_and_Traveller)
I believe (but can't find a clear source) that there are also Native American groups that prefer to be called Indian. This is a close analogy Egypt <-> Romani, India <-> Native Americans.
But it is true that many people only recently stopped using "gypped" as a slur. My kid was reading A Wrinkle in Time and looking for vocabulary words the other day, and I had to tell her that "gypped" was probably not appropriate for her homework and that we don't use that word anymore. So that's one reason to be aware that "Gypsy" is controversial. In my experience, many people are not aware of this fact at all because it so rarely comes up.
I'm inclined to think the author is aware of modern preferences, and that Stevenson's family may have referenced themselves this way.
In the US there are “Gypsy” and “Irish Travellers,” with the latter being a specific subset like Roma, and even then I’ve only heard the term used regionally, e.g. in Augusta, SC where a population lives.
Granted my sample size is O(100), but that's not nothing either. Although I tend to roll in more progressive circles.
It’s also a bad editorial decision. Here we are debating the headline and not even talking about the article.
Your reaction to a thing comes from you, not from the thing.
Both typical around these parts.
I suspect the author or publisher may have chosen the name of the book for that attention-drawing controversiality. RLS was not the healthiest author and partly 'wandered' in search of better prospects than those of Old Blighty.
So this editorial decision might be just part of this overall trend.