It probably has to do with 'cavas' being defined as a dependency in package.json, but the package.json file is meant for NPM.
That's correct. It's an invalid component since it's missing a component.json file, which is required if a component has dependencies. You can ask the author of Paper.js to add a component.json file, or fork the repo and add it yourself.
In addition their git tags, which yeoman install
(Bower) uses, are invalid semver (v0.22
while the valid notation is 0.2.2
). This will cause it to not work.