GDP is the measure of the value of goods and services a country produces every single year. Net worth, on the other hand, is a measure of how much capital a person has. They're two fairly different things. GDP is, in a simplistic way, a measure of income, whereas net worth is a measure of wealth. It's like saying my I have more equity in my house than you make in a year. It's like, well, yeah, that might be true, but it doesn't really mean you're more well-off than me.
Now if Mark Zuckerberg's income was higher than the GDP of Austria (or if his net worth was higher than the sum of all the capital in Austria), then I'd be impressed.