They don't make it at all clear on that bicycle site. However if you buy something from them and proceed through the various steps of the transaction you arrive at a Thawte certified page which actually carries out the transaction for you.
The issue for me is that you have entered your cc details just prior to this stage, so that the bike site can transfer those details to SEC pay (who does the CC checking thing) The problem being that until you arrive at the SECpay page the transaction is not necessarily encrypted so the CC details potentially have been transmitted without encryption.
Cheers Mike