Yes, you’re thinking along the right lines.
Resource bundles don’t have to use property files – it’s just one implementation (PropertyResourceBundle). A properties file is really just a string-to-string mapping – and that can be used for i18n, but doesn’t have to be.
ResourceBundle gives you a consistent way of requesting the appropriate object (usually a string) for a particular locale, with fallbacks etc. This is often, but not always, backed by a separate property file for each language.
So yes: if you’re dealing with i18n, you should use ResourceBundle; if you just need a string-to-string map persisted in a text file, it’s fine to use Properties directly.