It is geometry based. It has plenty of limitations of course, but can be really useful for detailed repeating patterns - fabrics being a great example, but it could be any element /surface with repeating geometry. The clever element is that the geometry patch fully conforms to the shape of the geo on which it is applied.
Here's a link to the info from the FStorm render - which was the first to offer it (2019?) as far as I know.
https://fstormrender.com/manual/geopattern/
I'm not sure where the original research paper came from, but someone recently suggested this one:
https://www.researchgate.net/publication/220792183_Relief_mapping_of_non-height-field_surface_details
- I haven't read the paper myself so I don't have any opinion if it's the correct source, but the visuals look similar.