How and to whom Allah gives knowledge is left to Allah to decide. Our duty according to the Quran is to follow only the Quran, as was the duty of the Last Messenger.
To go to 'other', none Quranic revelation for 'knowledge' because the beliefs and practices that someone has is not in Quran, is going against the Quran and is regarded as ancestor worship.
If we accept that the friend of Moses, youth was real, then him passing knowledge to Moses is confirmed by the Quran. This is not the case with the so called rites of Abraham that muslims believe are not in the Quran but must be followed. More ancestor worship!
18:60 And so, in the course of his quest for knowledge, Moses said to his young friend, “I shall not give up until I reach the junction of the two streams, though I march on for ages in my quest.”
[The Divine revelation shows the way and the outcome with conviction. When Moses was a young man, not yet commissioned as a Prophet, he was constantly in search of truth 93:7. God chose His Prophets and assigned them their mission at the appropriate time. The young Moses knew that the human intellect was the source of conceptual knowledge whereas the Divine revelation is the extrinsic knowledge from beyond human faculties. Intellect and revelation: The Two Streams of knowledge]
18:61 But when Moses with his young friend reached the junction of the two streams, they forgot all about the fish. And it disappeared into the sea. [Moses became more concerned about his people in bondage. Interestingly, fish is an ancient symbol of worldly life with all its glitter and ingulgence]
18:62 And after the two had walked some distance, Moses said to his young friend, “Bring us our lunch, the journey has been tiring.”
18:63 Said his friend, “Would you believe it? When we rested at the rock, I forgot about the fish and none but Satan, my wandering thoughts, made me forget it. And it took its way into the sea. How strange!
18:64 Moses said, “That is what we were seeking!” And the two turned back retracing their footsteps. (Moses retired to rest in deep thought.)
18:65 (Moses wondered how exciting the merging of the two streams would be! And he imagined that) he found a servant of Ours, upon whom We had bestowed grace from Our Presence and to whom We had imparted knowledge from Ourselves.
[A close examination of verses 60-65 is quite revealing. From this point on the young friend suddenly disappears. Also consider the way the fish disappeared, and how then, Moses remarks, "That is what we were seeking". I agree with Muhammad Asad that the 'fish' here is only figurative. I also understand that the young friend of Moses is none else but his own youthful enthusiasm taking him to a great quest. Then in 18:64 Moses goes back retracing his footsteps. So, what happens next is most probably his deep contemplation at rest. The mystical story is worth pondering. The enlightened man who meets Moses at this juncture, and later his weird actions, grant him an allegorical and not a tangible presence. For these reasons I think that in 18:60-82, the Qur’an is relating the intellectual search of Moses rather than his physical experience]
18:66 Moses (deep in his contemplation) said to the man, “May I follow you that you may teach me some of the knowledge and guidance which you have been taught?”
18:67 He said, "Surely, you would not be able to have patience with me.
18:68 And how can you bear with what you cannot comprehend?"
18:69 Moses said, "God willing, you will find me patient and I will not disobey you."