Around 30 minutes later I went on facebook.com, and saw an ad to this specific service.
Some context which I think controls for "simpler" explanations to this co-occurrence: I did not go on this service's website following our chat, nor did I search for it on Google. I did open the service's app on my phone, but it was already installed and as far as I know (and hope) Apple does not share this kind of usage data, let alone with Facebook.
WhatsApp chats are encrypted end-to end. My buest guess is that Facebook is able to do some kind of homomorphic encryption, which it was claimed to be able/trying to do [1,2].
[1] https://www.macrumors.com/2021/08/03/facebook-researching-analyzing-encrypted-data/
[2] https://www.androidauthority.com/whatsapp-encryption-ads-2728774/
Some simple explanations from there on out:
- your partner searched for the bike service or just any bike services and they happen to be the best fit for ads. More so, if you mentioned it to any friends, they could have searched for it and Facebook can associate relationships.
- neither of you may have had an original thought when the discussion of using the service came up. You maybe heard the idea in passing and/or were in an area where others were searching for it.
Facebook doesn’t need to know what you talk about, as much as they need to know who you talk to and building relationship models from there. Everything after that is simply extrapolating that you have interests similar to the people you interact with regularly OR to the people who go to the same places as yoy
So when you opened it you showed some intent that was deemed interesting enough.
Even if message content is encrypted end-to-end, I'm curious if those previews it loads are tracked.
Just curiosity. Can't really say they are, but it might explain something.
I think it's just a coincidence.