The main difference between Queso Fresco and Queso Blanco is in the ingredients and what it's made from.
Queso fresco is made with rennet and queso blanco is made from milk that has been curdled with an acid like lemon juice or vinegar.
The names queso fresco and queso blanco are commonly used interchangeably by some people but they are different.
It's basically the ingredients and how it's made that makes queso fresco and queso blanco different from each other.
They do taste similar in my opinion though and both are delicious.