If you go through old CS OS texts on the matter, they really didn't have the same understanding of capabilities then as the later object-capabilities (ocap) model would introduce. Typically they would show an access control matrix, note that acls were rows and capabilities columns and note that they are duals of one another. They're the same, acls are easier to manage, done.
OP is arguably the first paper that introduces ocaps. Some of the issues are discussed in "Capability Myths Demolished" https://papers.agoric.com/assets/pdf/papers/capability-myths...