Holds don't really show up in the monthly statement. At least not in the cards I've had. It's a functionality for merchants to say "I'd like to charge this customer up to $500, would she be good for it?". If the CC company says yes, then the merchant knows they can do so. E.g. car rental companies do this for potential damages. Up to a week the merchant can charge the actual amount (usually less) or just release the hold.
Holds are a credit card feature, GVB is a Dutch transit authority, so they're more likely to be talking about bank cards, ie. debit cards, which I don't think support holds in that same sense.
