Let's look at their equations and solutions one at a time.
Lena-Jon's equation, is a proper radical equation because she has at least one variable under a radical sign. Additionally, she has solved it in a proper manner by squaring both sides and tested her solution.
Ron-Jon has solved the equation correctly and tried his solution, but has not formed a radical equation. This is because he did not put any variable under the radical sign, only numbers. Therefore, it is Ron-Jon who made the error.