because it start with no prior knowledge at all it also has basically not understanding of the words you are saying so it's repeating to see what a normal response to a statement would be, it can learn for example
Session 1
Me: Hi
AI: Hi
Me: Hi how are you today
Session 2
Me: Hi
Ai: Hi how are you today
This is just a best case scenario, but from the ai getting that response from you it learned that "Hi how are you today" is a possible response to hi, and it can learn and grow from this same logic