Do you have already download the specification? https://www.oasis-open.org/standards#opendocumentv1.2
Here some quotes from section 3.15, part 1.
In 3.15.2 office:styles
The office:styles element contains common styles used in a document. A common style is a style chosen by a user for a document or portion thereof.
In 3.15.3 office:automatic-styles
The office:automatic-styles element contains automatic styles used in a document. An automatic style is one contains formatting properties that are considered to be properties of the object to which the style is assigned.
Note: Common and automatic styles behave differently in OpenDocument editing consumers. Common styles are presented to the user as a named set of formatting properties. The formatting properties of an automatic style are presented to a user as properties of the object to which the style is applied.
In short, office:automatic-styles corresponds to direct formatting of an object and office:styles correspond to the settings via style&formatting window. Although automatic styles “are considered to be properties of the object” it is not forbidden to use the same automatic style for more than one object. You have no UI for doing so, but you can do it in the file itself.