So both Adam and Noah are known (other than through repetition of their stories in the Qur'an and affirmation of their status as Manifestations in Baha'u'llah's writings) only on the basis of a completely fabulous and intentionally symbolic mythology written, it is supposed, by a descendant of both of them - which now becomes relevant because if they really existed, they were not, as claimed in the Biblical tradition, the actual progenitors of all humans.
Manifestations of God are not just manifestations of human knowledge. They can at times access the knowledge that is with God, the All-Knowing.
In fact, there were probably millions of humans around the globe at the time they existed, but God - in his desire to promote unity and peace - chose to select Manifestations in at least 7 "Dispensations" from the same small semi-nomadic tribe in an otherwise insignificant corner of the middle east, namely, Adam, Noah, Abraham, Moses, Jesus, Muhammad and Baha'u'llah himself?
There is also Krishna, Buddha and undoubtedly many other Manifestations of God that we don't know about as they have been lost in the mists of time. Then there are innumerable prophets, sages, and people of great capacity that have had profound influence.
One lesson from the myth of creation in Genesis, is that God is concerned for His creation and man. An All-Loving, All-Powerful and Just God is not just concerned for one people, but for all peoples.
Now what of Abraham? Was he a real person or just a name associated with a symbolic story? He is, after all, recorded as having lived 175 years - only slightly more plausible than Adams 930 and Noah's 950 - being more than 50 years longer than any properly verified human life-span.
Abraham is consider to have been a real person. I wouldn't take the years of His lifespan too literally either.
"The years of Noah are not years as we count them, and as our teachings do not state that this reference to years means His dispensation, we cannot interpret it this way."
(From a letter written on behalf of the Guardian to an individual believer, November 25, 1950; quoted in Lights of Guidance, no. 1659)
So - where in the genealogy in Genesis 11 - is the line between fable and fact? And if the story of Abraham (and his wives and concubines) is also symbolic - as the Bible itself suggests in Galatians 4:24 - what value should we assign to the Baha'i claim that Baha'u'llah is a descendant of Abraham.
Only God knows for certain. There is nothing in either the Bible or Baha'i writings that suggests the genealogy outlined in the Bible is incorrect.
"Thus it is an especial blessing that from among the descendants of Abraham should have come all the Prophets of the children of Israel. This is a blessing that God has granted to this descent: to Moses from His father and mother, to Christ from His mother’s line; also to Muḥammad and the Báb, and to all the Prophets and the Holy Manifestations of Israel. The Blessed Beauty 1 is also a lineal descendant of Abraham, for Abraham had other sons besides Ishmael and Isaac who in those days migrated to the lands of Persia and Afghanistan, and the Blessed Beauty is one of their descendants." – Abdu'l Baha, Some Answered Questions p.213
Abdu'l-Baha was appointed by Baha'u'llah as authorised interpreter and expounder of His words.