Ask HN: Ads triggered by WhatsApp “end to end encrypted” messages?

Hi all. We've been playing a silly little game with my wife lately: we send each other messages about some topic we never talk about and then wait for ads related to our conversation to start showing up in Instagram. As of the last month, they never fail to show up.

Please keep in mind that this is a conversation between two "personal" accounts, no business accounts involved. More so, we haven't accepted the new terms of use that "allowed" WhatsApp to access messages between personal accounts and business accounts.

Is WhatsApp scanning personal messages to target their ads as we are noticing? Weren't WhatsApp messages end to end encrypted? Is this a violation of their Terms of Use or am I missing something silly?