"He is thirsty."
Translation:Er hat Durst.
You must differ: "durstig" is an adjectiv, "Durst" (der) is a noun. In German you have the structure "Durst/Hunger haben" but you can also say "hungrig/durstig sein". It is actually a little bit more common to use "Durst/Hunger haben" than "hungrig/durstig sein" and I guess that's why they chose this translation.
So I'm having a bit of trouble here when I see this simple line. I mouse over "is" and it shows up as "ist" so i type in: Er ist Durst (because ist means Is in german, thats what it says" and i get it wrong. hat/ist same thing??