Ask HN: What happens to the 2% Zillow “contributes” to its 1% down mortgage?

Zillow is "offering" a 1% down mortgage:

https://www.zillowgroup.com/news/zillow-home-loans-new-1-down-payment-option/

However, the minimum down payment that Freddie Mac will buy and securitize is 3%:

https://myhome.freddiemac.com/buying/down-payments-and-pmi#:~:text=The%20reality%20of%20down%20payments&text=What%20most%20people%20don%27t,®%20or%20HomeOne®%20mortgages.

This 2% gap is made up by Zillow, who claims to "pay" the other 2%:

Borrowers who qualify can now put just 1% down on a home, and Zillow Home Loans will pay the other 2%.

I find that hard to believe. Impossible even.

I can't find anywhere the true story behind this 2%. Right now my leading hypotheses are:

1. It's really a second lien and you have effectively borrowed those 2% from Zillow. 2. They jack up your rate (within the allowable rates) such that when they sell the loan to Fannie/Freddie they get the 2% back. 3. They "own" 2% of your home in equity (like Hometap, https://www.hometap.com).

Anyone have a clue?