I had a French lady friend in Texas. She was fond of the music of this one Cajun-descended local singer/songwriter.
Once at a concert of his, another Cajun came up to her and started speaking in Cajun French.
She understood him with some difficulty, and it dawned on her that it sounded like a very old dialect of continental French.
I was talking with a Cajun aquaintance last week who said exactly the same thing - the local patois is different from continental French because it has been spoken in relative isolation since the seventeenth century. They say the same thing about the Quebecois dialect.