Clarity means that your message should be easy to understand. The first question he asked is whether the ideas are understandable or not, this indicated the very definition of clarity. In second question he's asking whether he used plain English and familiar words, again this means he's emphasizing that whether he has included words which are easily understandable for the receiver. And in the last part he's asking whether his message need further explanations which again means he's talking about clarity in the message.
