Eh, this is a very particular and long-standing racist term, and the meaning used by the authors is derived from the slur, so it's not incidental.
There's also rather significant modern use of "tinker": https://en.wikipedia.org/wiki/Tinker_(disambiguation)
It appears that you're getting stuck on "tinkers", which is mentioned in the above disambiguation page:
> Tinkers, an alternate (and often pejorative) name
Anyway, language is malleable and changes. In this case, I will again emphasize "get a life."
Eh, this is a very particular and long-standing racist term, and the meaning used by the authors is derived from the slur, so it's not incidental.