Come on. You do not tell them you don’t know. It was a 6 month assignment. Grow up and move on.
“Grow up and move on?” That’s a mean response.
The same happened to me not long ago; take heart that old employers don’t share much with new ones and YOU are in control of the narrative.
In my case what I did was reached out to a colleague who wrote me a stunning recommendation letter.
I, too, was never told what had happened or why I was let go, and I was devastated.