Hello @Jeroen Vormer 

That incompatibility means exactly that you have a new (and in this case a major version) version of Charts that is not the same referenced in that OutSystems UI Style Guide Preview version - this is calculated by Forge.
The references in the OutSystems model don't change dynamically, ie, each version of each component stores the producer's version at the moment of the deployment to Forge which only works almost as a repo for these artefacts. Also, for these secondary assets, the release cycle isn't the same as for other assets.  
For possible impacts, you should check the producer release notes and check if they can impact you (which in this case I don't think it will).

Cheers,
GM