I can assure you that my American Express is marked as a credit card everywhere, even though it autopays itself automatically at the end of each month.
You may want to review the fine print. AMEX offers both types of card, but "credit card" and "charge card" (sometimes "purchasing card") are meaningful financial terms. AMEX used to offer primarily charge cards back in the day, but they've changed many of their cards to credit cards these days.
Does your particular card offer credit as a feature? This is how some of the US cards are, they sort of position the credit feature more like an "option" compared to what other issuers do. Because it is offered at all, it is a credit card, even if you pay the full balance normally.
FWIW, all the cards I see on their French site are described as:
