What is the meaning of this sentence?

First, is he a Dr Thomas or a Mr Thomas. That would make a difference. If, as he is addressed first, he is Mr Thomas, it can have two meanings. The first meaning is that he is not available as a close family member / members (or friends) has / have been involved in an accident or taken seriously ill. The second meaning is that Mr Thomas may have had a serious accident or taken seriously ill (heart attack etc.). In either case, the secretary had no right to divulge that information as it could cause some distress to Mr Thomas and / or his family. All she needed to say was that he wasn't available. As for Dr Thomas, it is highly likely that he has been called out to a sick patient. Before posting this sort of question, make sure the information needed is clear, otherwise you may not get the correct answer.