Most issuing banks charge a small fee (usually something in the range between 1 and 2.5%) for foreign credit card transactions. This has nothing to do with the currency, but rather with the charging entity being in a different country/payment area than the issuing bank. In this case, the issuing bank is most certainly within SEPA, while the charging entity is located in the US.
So it’s probably not a conversion charge but rather one for international payments, which is collected by the bank/credit card company rather than Framework.