I don't think I would be quite sure what this employer was looking for either. jQuery of course manipulates lots of objects, especially DOM objects, but the vast majority of jQuery code is written in a procedural style. There's no object type hierarchy or composition. There's just the one, monolithic jQuery object type. Not even jQuery.extend does prototypal inheritance. It actually just copies properties from one object into another.
If you want to see what real OOP principles looks like, you should check out other libraries such as YUI, Dojo, or ExtJS.