Thanks for joining, and thanks for your question!
From what I can tell, yes, the site you originally linked to (which I removed) appears to be in the United States and therefore likely intended for U.S. cardholders only. Your profile indicates you are in the U.K. Most banks and credit card companies do maintain separate systems per country, for legal reasons.
Anyway, for your own security I suggest you contact your card issuer's support telephone number and request the correct U.K. cardholder web site address from them directly.
In general, you don't want to be guessing or searching for the web site address for your credit card company or bank's online self-service application. There are often "impostor" web sites out there that just want your credit card number!
Instead, you should obtain the web site addresses for your financial services from trusted sources only; i.e. direct from your bank or card issuer, such as on your printed statement, or through their help line, or linked-to from their known-good home page.
Finally, I do believe that your credit card number and account number are one and the same thing.