>> the sum of the squares of those numbers have a difference of 200

Did you see this problem in official print or verbally or in notes?

"sum of the squares of those numbers" is a common math expression meaning:

(X squared + Y squared)

whereas your expression: X squared - Y squared might be read as difference between two squares.

If you can get a look at the text of the official problem, it would be interesting to see if it matches your statement.