I think there's a subtle difference between those two things, though. The first one is a matter of roles: if you own a cookbook, you may transfer ownership. The second one is a matter of existence: if you own a cookbook and Gabe is the only collaborator, you are authorized to transfer ownership of that cookbook, but the only possible transfer by the Rules of Supermarket™ is the transfer to Gabe.

The language is the biggest tip-off to me. It feels odd to say that the user is authorized to transfer the cookbook collaborator (which is roughly how I read the current code). It feels much more natural to say that the user is authorized to transfer the cookbook.