An affidavit/affirmation does not make your marriage valid under UK or foreign law, or guarantee to the local authorities that you are free to marry. ..
What does this mean? Does it mean the marriage has not been legally recorded in UK like it would be if you married here?
Neither a CNI nor an Affidavit/Afformation records an overseas marriage in UK
The Affidavit/Affirmation is a statement from the applicant that the local authorities or British Embassy cannot be held responsible for.
Maybe the applicant is telling porkies.