I will add one more "alternative" to Esa Jokinen's answer.

Someone else around you did "give the information away".

Example...

You talked about a holiday in some place with your spouse. Your spouse did not mention it but did some research, using a shared computer for instance, maybe even using your mobile, using their own device with your account somehow logged in, or from the same IP address simply.

(There might be extra scenarios here, that's all I could come from within a minute).

Advertisers now know of some interest (they may think you're the one interest, they may not know precisely, or they might even know your spouse was the one interested!). And now they are advertising you that holiday.

Someone else around you could have "given the information away".

Example...

You talked about a holiday with your spouse. Your spouse did not mention it, but did some research, using a shared computer for instance, maybe even using your mobile, using their own device with your account somehow logged in, or from the same IP address.

Advertisers now know of some interest (they may think you're the one interest, they may not know precisely, or they might even know your spouse was the one interested!). And now they are advertising you that holiday.