Was the Abhidhamma taught by the Buddha?
Mendis refers to “Theravāda tradition”. His source is the introduction to the Atthasālinī, which was compiled by Buddhaghosa in about 400 AD based on earlier texts that no longer exist.

The Abhidhamma is a framework that consolidates teachings from more than 10,000 Suttas. This framework follows the Theravāda perspective. IMHO, the scholar’s view that the Abhidhamma was developed slightly after the Suttas makes sense.

Though the Abhidhamma may not be the literal word of the Buddha, it is extremely important. The commentaries, which explain the Suttas according to the Theravāda perspective are based on the Abhidhamma.

I once met a monk who had heard that I taught Abhidhamma. The monk said, “I have my own interpretation of the Suttas based on my own experience. It differs from the Abhidhamma and Commentaries.”

I replied, “Venerable Sir, I cannot say whose interpretation is correct. But if I follow your interpretation, then if I have any questions, I have only one source of reference... you. If I follow the traditional Theravāda interpretation, then I can refer to many books and many teachers.”

People who say, “I will only focus on the Suttas and ignore the Abhidhamma and Commentaries” risk misinterpreting the Buddha’s message! Unfortunately, I have seen many examples of this.