The orthodox Theravada position is that Abhidhamma- even the Katthavathu -is the word of the Buddha:
The atthasalini (Commentary on the Dhammasangani ,trns THe Expositor p.8) by Buddhaghosa discusses suttas that are part of the canon that are not spoken directly by the Buddha:
also:Bhikkhus, learned is Mahăkaccãna, profoundly wise is Mahăkaccãna. II you had asked me the same question, I would have ariswered exactly as he has done.' Thus since the time when the Teacher gave his approval, the whole Suttanta became the word o1 the Buddha. And it is the same with the Suttas expounded by Ananda and others.
'thus in teaching the seven books, when he came to the Kathãvatthu the Buddha laid down the table of contents in the way mentioned above. In doing ao he foresaw that two hundred and eighteen years after his death, Tisaa, Moggali’ø son, seated in the midst of one thousand Bhikkhus, would elaborate the Kathavathu as is stated above. And 'Tissa Mogali son, expounded the book not by his own knowledge but according to the table of contents laid down, as well as by the method given, by the 'teacher. hence the entire book became the word of the Buddha. Thus the Abhidhamma consists of seven books inclusive of the Kathavathu.
The textual order of the .Abhidhamma originated with Sariputta ; the numerical series in the break Book was also determined by him. In this way the Elder, without spoiling the unique doctrine, laid down the numerical series in order
*to make it easy to learn, remember, study and teach the Law. Such being the case, was the Elder the very first to understand the Abhidhamma ? Nay, it was the Supreme Buddha who first understood the Abhidhamma. For he, seated on the throne under the Wisdom Tree, penetrated if and became the Buddha