yes, it's a scaled version of a triangle with side lengths 3, 4 and 5.
by a factor of 20
a triangle with side lengths 3, 4 and 5 is a right triangle and it holds true for a²+b²=c², because 9+16=25
the 3,4,5-triangle is the simplest right triangle to calculate it's numbers seem somehow elegant.
the triangle in your problem is just a bigger version of it (wich means all angles stay the same).
My reasoning is lacking, but I'm sure
