Acknowledging that there was a historical development of moral philosophy that eventually led to the invention of secular humanism makes no difference to the basic assertion that secular humanism is a non-theistic system of morality.
You still need to explain what you mean by "morality without God".
What is that, "morality without god"?
"Morality without direct or indirect reference to existing theistic religions"?
"Morality that doesn't mention God nor refer to God as a justificatory instance"?
"Morality that is developed and pursued independently of God"?
"Morality that is developed and pursued independently of existing theistic religions"?
Acknowledging that there was a historical development of moral philosophy that eventually led to the invention of secular humanism makes no difference to the basic assertion that secular humanism is a non-theistic system of morality.
For one, humanists cannot even define what they are about, without referring to religion and God.
For two, however fancy and non-theistic humanist principles may be, they are nevertheless taken from theistic principles.
Free will, the worth of a human life, fundamental equality - none of these can be scientifically evidenced, nor argued for without reference to some higher all-overarching, all-encompassing principles.