God talks to him and gives him instructions. He then asks with whom he has been talking, and God says: I am 'that' I am.

Now, leaving aside the simply metaphorical element - i.e. a burning bush, it seems to me that Moses is experiencing a classic example of the mystical experience.

He is experiencing a lowering of his personal ego limitations, and a sense of belonging to a wider, far more acute reality, in which he is communicated with by a deep internal person or voice.

Though not exactly everyday, this experience is not all that rare, and has seemingly been known to many humans throughout recorded history, to the present day (human make-up hasn't changed within the same time period).

'Atman is then the spark of Brahman that happens to make you you

Yes. The stuff of the objective world (matter), when organised appropriately by the organism which is our physical body, gives rise to consciousness, to the "I am".'

In a sense there is a contradiction in this statement.

By accepting that Brahman makes us, one accepts that spirit is not a product of matter (i.e. atman pre-exists matter).

The organisation of the physical world also predates our own perceptions. It is never 'organised' by ourselves.
Our consciousness is a product of a natural ordering by whatever force creates us, to equip us to relate to a common physical reality, yet imparts us the equipment to perceive the greater consciousness which has made us.

That is, at certain times, the same experience which Moses had, and which is a classic periodic happening to certain people, is apparently a sort of gift, never of our making, which occurs by a volition beyond ourselves, yet which commonly is experienced as divine.