Not all pictures are representational, some are abstract or non-figurative. Not all representations are pictures or pictorial. Language is often held for example to be representational, to represent the world. Though there are many pitfalls in this idea.
Literature is a mimetic or representational art, so are sculpture, dance and drama.
Not all representational pictures are works of art , or don t purport to be works of art. Consider for example many photographs, certainly my holiday snaps, and advertisements. It is one thing to seek to understand the phenomenon of pictorial representation, which is what this lecture is concerned with, and another to make value judgements. Apart from this mention here, this lecture is not concerned with the topic of value judgements of representational works of art. Gombrich, we have come to understand just what an achievement a representational picture is, we shall not withhold our admiration.