So the Pythagorean Theorem is a^2 + b^2 = c^2. The error in the problem is that each term was multiplied by 2 instead of being squared. So the problem should be:
28^2 + 45^2 = 53^2 784 + 2025 = 2809 2809 = 2809
So the sides given do actually form a right triangle.