Yes, but we are talking about the situation 1000 years ago, when languages weren't standardized and, as a result, much more fuzzy. Today you can say where, say, German ends and Dutch begins; but it used to be a continuum. Same with French.
Even Medieval Latin spoken by the learned people was a bit different from Classical Latin of Cicero, and that was a language which was taken care of by educated, literate people. Vernaculars of the day ... well, tended to be different from region to region, because there was no one with enough influence and authority to codify them.
Looking at that situation, I am fine with classifying 11-th century Norman as "basically French". Mutual intelligibility was certainly fairly high. William the Conqueror would need no interpreter when talking to some Parisian merchant. There were some Norse leftovers present, but such was the situation everywhere.
Even Medieval Latin spoken by the learned people was a bit different from Classical Latin of Cicero, and that was a language which was taken care of by educated, literate people. Vernaculars of the day ... well, tended to be different from region to region, because there was no one with enough influence and authority to codify them.
Looking at that situation, I am fine with classifying 11-th century Norman as "basically French". Mutual intelligibility was certainly fairly high. William the Conqueror would need no interpreter when talking to some Parisian merchant. There were some Norse leftovers present, but such was the situation everywhere.