Good question, I do not know exactly. I would think that, since God is Spirit, infinite and transcendent, that whatever they saw, was just a material manifestation of his power. Not an avatar, as if God's being was literally behind the avatar, but like the cloud of smoke and fire that directed the Israelites way during the Exodus.
Just like Moses saw God's back, or Elijah saw God in the whisper. God does not have a back, and if he did, how big would it be, i.e. the size of the earth, Jupiter, the Milky Way, Orion, ...you get the point?
Whatever the elders of Israel saw, was so small and visible, that it clearly wasn't God, was it?
So, I really don't know, but what I do know, is that God is larger than the universe, and that he is not corporeal. Therefore, I would think that God just manipulated material matter in a supernatural way, that let those around him know that he was in their presence, that is, he was 'with them' and was acting in their favour.
John 4:19 The woman saith unto him, Sir, I perceive that thou art a prophet. 20 Our fathers worshipped in this mountain; and ye say, that in Jerusalem is the place where men ought to worship. 21 Jesus saith unto her, Woman, believe me, the hour cometh, when ye shall neither in this mountain, nor yet at Jerusalem, worship the Father. 22 Ye worship ye know not what: we know what we worship: for salvation is of the Jews. 23 But the hour cometh, and now is, when the true worshippers shall worship the Father in spirit and in truth: for the Father seeketh such to worship him. 24 God is a Spirit: and they that worship him must worship him in spirit and in truth.
Jesus saying "God is a Spirit" is not testifying that He does not have a celestial body. Jesus was talking to the Samaritan woman at the well in answering her question about where they are supposed to go to worship God at. Jesus said a time will come when worshippers shall come to God the Father to worship IN spirit and IN truth, and so God is a Spirit is inferring His omnipresence in the reality of the believer where He is with us always as IN the Holy Spirit & IN Jesus Christ so we can come to God the Father anywhere to worship Him by coming to and honoring the Son in worship. John 14:6 & John 5:22-23 & Philippians 2:5-13
As it is, and only God can help us see the truth in His words to grasp this; but the Father has a celestial body as the Son did before His incarnation for why the request to make man in "our image" and "after our likeness" in Genesis 1:26 was made and yet when God did perform the act by having made man in His image and after His likeness in Genesis 1:27, He did so as the Three Witnesses within the One God in establishing a word in creation by the Word of God.
Jesus did say that in the future, we will not need to ask Him to ask the Father for He will openly show us the Father to ask Him directly.
John 16:24 Hitherto have ye asked nothing in my name: ask, and ye shall receive, that your joy may be full. 25 These things have I spoken unto you in proverbs: but the time cometh, when I shall no more speak unto you in proverbs,
but I shall shew you plainly of the Father. 26 At that day ye shall ask in my name: and I say not unto you, that I will pray the Father for you: 27 For the Father himself loveth you, because ye have loved me, and have believed that I came out from God. 28 I came forth from the Father, and am come into the world: again, I leave the world, and go to the Father.
Hard to imagine but if we picture being in the bosom of God for where He is, would we be inside of that Triune God to see Two of the Three Persons in that One God? I do wonder, and maybe we will all know for sure when we see Him face to face and not just the Son's.
As it is, God is a Spirit is being applied wrong by many believers and churches when it is about being able to worship God anywhere now and when the request for us to be created was in a plural sense, signifying that God has a body too, we really should believe that, regardless of being hard to understand.
Isaiah 55:8 For my thoughts are not your thoughts, neither are your ways my ways, saith the Lord. 9 For as the heavens are higher than the earth, so are my ways higher than your ways, and my thoughts than your thoughts.