Feta Cheese and Goat Cheese are similar because they both do contain goat milk but Goat Cheese is 100% goats milk while Feta Cheese does contain goat milk but also contains Sheep's Milk.
Feta Cheese Contains more Sheep's Milk than goats milk.
So goat cheese and feta cheese do contain goats milk but goats cheese is 100% goats milk while feta cheese is partial goats milk but around 80% sheep's milk.
They're sometimes mistaken for the same type of cheese but they're different and feta cheese usually tastes a bit different than goats cheese.
They're both healthy cheeses and are good alternative cheeses for people allergic to cows milk.