I've looked into this and also replied to them. They haven't kept updating their project to subsequent Spine versions. The project appears to be made with one of the 2.x Spine versions and will require manual fixing on their end, e.g. change flip x/y using negative scale. I've emailed them about this, sorry for the inconvenience.
FWIW, the asset opens up in the latest Spine, we just display a warning dialog to signal that there are things in the project that need fixing in later versions.