I think that might be your interpretation of the line but I don't think that is what Bart intended when he wrote it. As I recall, when Oliver tells Dodger that he has no mother or father. Dodger says "Lovely" because this is good news for him as he has just found a new pick pocket for Fagin. But, as soon as he says "Lovely" he realizes that would not sound right to Oliver and it might give up Dodger's real motivations which is to recruit Oliver for Fagin. Therefore, he says "Lovely", realizes what he is saying and quickly fixes his slip-up by changing the topic to the weather; "Lovely......balmy weather we're having today." "Lovely bastard" would not make sense as the a in "bastard" and the a in "balmy" do not make the same sound.