Agreed, it does not seem to be clear. See these threads, for example:
https://forum.inaturalist.org/t/my-observations-are-missing-from-gbif-and-am-not-sure-why/37311
There is an argument that facts themselves can’t be copyrighted (date, time and location of a species observation) and so this license applies to comments and notes. But it’s not 100% clear, and GBIF takes a precautionary approach by not accepting even the bare metadata for observations with more restrictive licenses. I put CC0 for my observation license and CC-BY for photos and sounds.