I'm thinking that Jan Koum might be a way MZ is selling "additional holdings. Jan Koum is a Ukranian who designed WhatsApp. Rags to Riches story - literally. In 2014 Koum and co-founder Brian Acton, another former Yahoo employee, sold WhatsApp to Facebook in a deal worth $19 billion. Today Koum is worth $9.3 billion.
He's been selling stock right alongside MZ. Do you think he owes Mark??!! I'd say so. Insider trading too, I imagine.