That's very interesting. So another story in the Bible that Baha'is don't believe is "authentic". So Samuel never told Saul those things about the Amalekites? Or, God never told Samuel to tell Saul those things about killing everybody?
Are you absolutely sure about the things that Jesus affirmed about stories in the Bible? Or, since the NT is not wholly "authentic" either, would those things be the gospel writers putting words in Jesus' mouth?
Know ye that the Torah is that which was revealed in the Tablets to Moses, may peace be upon Him, or that to which He was bidden. But the stories are historical narratives and were written after Moses, may peace be upon Him.
(From a previously untranslated Tablet)
The Four Gospels were written after Him [Christ]. John, Luke, Mark and Matthew - these four wrote after Christ what they remembered of His utterances.
We have no way of substantiating the stories of the Old Testament other than references to them in our own teachings, so we cannot say exactly what happened at the battle of Jericho.
(25 November 1950 to an individual believer
We cannot be sure of the authenticity of any of the phrases in the Old or the New Testament. What we can be sure of is when such references or words are cited or quoted in either the Quran or the Bahá'í writings.
(4 July 1947 to an individual believer)
When 'Abdu'l-Bahá states we believe what is in the Bible, He means in substance. Not that we believe every word of it to be taken literally or that every word is the authentic saying of the Prophet.
(11 February 1944 to an individual believer)
The Bahá'ís believe that God's Revelation is under His care and protection and that the essence, or essential elements, of what His Manifestations intended to convey has been recorded and preserved in Their Holy Books. However, as the sayings of the ancient Prophets were written down some time later, we cannot categorically state, as we do in the case of the Writings of Bahá'u'lláh, that the words and phrases attributed to Them are Their exact words
(9 August 1984 to an individual believer)
The Bible