I doubt that was the intent at the time. Sure they'd be looking for ways to monetize, but could the co-founder in 2012 have predicted what FB as an entity would become ~10 years later?
I’m not blaming them for selling out for $20B, I would have done the same. But I won’t believe they didn’t know what was going to happen.
I don't fault them for selling, I fault everyone else for assuming it would always be ad free after the sale.
This is the timeline as I recall it (and from quickly googling a couple of articles), feel free to correct me if I'm getting things wrong:
2012: this article
2014: FB acquires whatsapp
2016: Whatsapp becomes free (drops the $1 purchase fee)
2018: Jan Koun and Brian Acton leave FB