SCJ teaches that Adam is not the first man. But he was the first assigned pastor/ shepherd.
They believe that there is a pastor for each era who leads God's people. (Adam- Noah- Abraham- Moses- Jesus). This pastor delivers the word of God and brings salvation to His people.
They say Adam is not the first man because of the following reasons.
Cain was afraid of being killed by others when he was expelled by God. This means that there were others other than Abel and Cain (Gen 4:14)
Cain married a woman when he was away from home. (Gen 4:16-17) There was a woman outside of Adam's family.
However, this is what the Bible says what happened:
There was no man before Adam (Gen 2:5)
Then Adam was formed by God from the dust (Gen 2:7)
Adam had Cain and Abel (Gen 4:1-2)
Cain killed his brother (Gen 4:8)
Then Seth was born later in place of Abel (Gen 5:3-4)
There seems to be no other comments mentioning about other men.
It is possible that he could have other sons and daughters before Seth. Not all sons and daughters are mentioned in the Bible.
After Seth, Adam and Eve had a lot more children for their 900 years of life. There were other sons and daughters
Cain could have married another woman of his own family.
Ex) Abraham and Isaac also married their own family. They intermarried within their own family.
But I admit that these are the possibilities and not directly mentioned in the Bible
The Bible doesn’t directly mention whom Cain was afraid of, or whom Cain got married to.
But here are the facts that the Bible records:
There was no man before Adam. (Gen 2:5)
Adam lived 800 years and had other sons and daughters (Gen 5:4)
Now I want to change the topic to this: was ADAM really the first pastor that SCJ is talking about?
According to SCJ, the chosen pastor for each period is the one who leads God's people to God. But there is a BIG problem. Adam didn't lead His people like he was supposed to as the first chosen pastor! He was the first one mentioned in the Bible who rather committed sin and fell.
Another angle:
According to SCK, the tree represents a person/ shepherd/ pastor (Isaiah 5:7). Each promised pastor is considered as the tree of life for each period of time.
There are two trees in the garden of Eden. The tree of life, and the tree of the knowledge of good and evil (Gen 2:9)
While Adam was to be the shepherd of God for his time, and he is the good tree for his time. But this good tree, Adam, went to eat the fruit from the forbidden tree. (Gen 3:6)
It is a complete contradiction that Adam was the good shepherd of God in his time. He was definitely not.
What is really the purpose of SCJ saying that Adam was not the first man?
They are trying to introduce the concept of a pastor/ shepherd for each time. So that there is also the pastor for today's time--Man Hee Lee.
God did not say there were other men before Adam, and that Adam was just the appointed pastor for the first time. There was no man before! (Gen 2:5) And He created Adam out of dust (Gen 2:7)…
Genesis is merely trying to describe how God created the world and how things all started from the beginning.
SCJ tries to spiritualize things and downplay the story of creation. They emphasize on spiritual meanings of each word, which they plug in other parables and the book of Revelation to describe the promised pastor at the end. The promised pastor is their ultimate goal/end for all their teachings. Our true shepherd: Jesus (John 10:11)
The thief comes to steal, kill, and destroy. (John 10:10)
In original language, the word steal is to steal "secretively"
We are to focus on Jesus
No need to have another pastor to come after Jesus when He Himself has promised that He will come back again. He did not say He will come in spirit working in someone else's body.

Image from: http://www.ingodsimage.com/wp-content/uploads/2013/09/Creation-Museum-18.jpg