The headline is kind of misleading, as most people are likely to read it and go 'well duh, fossils are rock'. It means a specific set of fossils aren't of plant nor animal. Stripping the 'Bizarre' from the start of the sciencealert headline creates the misleading parsing.
The OP article headline is still misleading. s/were/are/ would help. And HN should s/Bizarre/Some/ instead of deleting the word.