But does this imply that a sexaquark may itself be a dark matter particle?
The guy is stable and very weakly interacting (it does not couple to most particles). Those are the basic properties for a dark matter particle. Its properties then allow it to escape all direct dark matter detection bounds, and it could even help to explain star formation.
So, if the sexaquark exists (it is so far predicted theoretically but not observed), it could satisfy all the requirements of dark matter.