I usually just say " odd, i cant seem to find that one"

In most places its not legal to serve yourself alcohol you brought to the restaurant yourself. So as a compromise many restraunt owners will allow you to bring a bottle of wine that they dont carry, and then charge you a fee to serve it to you. This means they are staying within the law with respect to liquor laws.

For example where I it is illegal to give away alcohol tor free. If a restaurant serves it to you, even if you purchased it before hand, they would be serving it for free and thus a violation of the liquor laws; hence the corkage fee which allows restaurants to so serve you your wine within the law.

https://www.touchbistro.com/blog/corkage-fee/

A few charged for opening a bottle of wine. It used to only be charged if you brought your own bottle to the restaurant.