So not only are you alleging that Meta scans your whatsapp messages for advertising purposes (which they strongly claim they don't do), you are also alleging that they are selling your whatsapp messages to Google?
That's some serious accusations. Without strong proof I don't believe it.
I assumed they were saying that they'd received an email ad, not that google served an ad. I could be wrong though. I wouldn't trust what meta says here considering their past history, but there are reasonable alternate sources in this case. Keyboard replacements on phones are notorious for logging, or either participant could have an app logging screenshots.
That's some serious accusations. Without strong proof I don't believe it.