At the risk of sounding elementary ......
There can easily be some differences in communication styles going on here.
The way that I was raised ... if I were hosting such an event and you offered to bring something the polite response is so say, "No, that's fine." If the offeror truly does wish to bring something, the offeror responds to this by saying something such as, "It's really not a problem and I would like to bring something." The host then replies, "Well if you insist, ..." and then makes a suggestion of what to bring.
This exchange recognizes the "polite offer". If someone invites you for dinner, you are obligated to offer to bring something even if you really don't want to. On the other side of the exchange, as a host you should not extend an invitation with strings attached - you should be prepared to provide all of the preparations. If the guest is truly willing to bring something and the host is truly willing to accept then that exchange is also negotiated via an exchange such as this. The niceties are fulfilled and hopefully everyone has an acceptable outcome.
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That type of exchange was automatic in the social circles in which I was raised. I also now know that type of exchange is not automatic among many people here in the US. In this social protocol, you don't offer to bring something unless it is a sincere offer (i.e., there is no such thing as a polite offer) and the host declines any offer if the host truly does not want help.
That exchange also works fine if that protocol is common to the parties.
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Problems can occur when one party uses one style, while the other adheres to the other. The situation being discussed is rife with opportunity for miscommunication if the principals have differing protocols.
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And if they are wine drinkers and you know nothing about wine, then wine is probably not a good gift. You should stick with items you know.
In the situation at hand, bringing a small box of chocolates could be appropriate. Or some fresh cut flowers to put on the table. Others may have additional ideas.