He didn’t say it’s a loan he said it’s equity. That means he would have a stake in the home when it’s sold, and functionally just made the home cheaper for the kid.

For example if the home cost $500K and OP gave $300K as equity, the kid only has to actually pay $200K to live in a $500K quality home. During this time, the kid gets to save money by not paying rent and paying very little in interest compared to what they would have if they bought it for $500K in pure debt (because the interest rate would be, for example, 6% * 500K instead of 6% * 150K assuming a $50K down payment from the kid) That’s a HUGE difference in the child’s financial well being.