...who has just started practicing spoken Japanese to make...
I thought そして、初心者だった時に間違えませんでしたか？ was more suitable.そして、初心者だった時に間違えませんでしたか？＝You are sure that the readers have made mistake, too.It's called 反語 in Japanese. We learn at school that （いや、間違えたに違いない）is concealed.