I think it's wrong, and either calmbonsai is speculating or just colloquially using "trust fund kid" to mean coming from a wealthy family.

That is, Ferris's family was undeniably well-off. From some quick research it looks like his dad was a pharmaceutical exec, his mom was a small gallery owner, he grew up in East Hampton and went to an expensive prep school. But I couldn't find any evidence that he received a large inheritance or had a literal trust fund. So yes, like a lot of people who become rich, it looks like he could afford to take risks, but his financial success flows from his own work and investments.

People have to stop believing Google's AI overview - it can be a useful pointer to other sources but it still makes shit up all the time. In this specific instance, the overview says "Father's Philosophy: His father, a high school graduate, emphasized simplicity in business, famously describing it as three shoeboxes: money in, money out, and profit." Except the link there goes to a page where Ferris was quoting someone else (Nick Kokonas) about Nick's father, not Ferris' own dad. It's flat out wrong and typical AI slop.