The original developer is trying to do things slowly and stay with older versions of the dependencies, while the author of the fork is of the opinion that the dependencies should be updated to the latest versions and take advantage of their capabilities (such as performance improvements) which does not necessarily please the original author.
In addition, new features are implemented in the fork that are not present in the original project, because the author of the fork is pushing for rapid development (which doesn't mean it's a bad thing)