How is this nonstandard equation solved?

Here is a serious achievement of the Roots command:

Student[Calculus1]:-Roots(2^x+3^x+6^x-x^2);

                              [-1]

plot(2^x+3^x+6^x-x^2, x = -6 .. 2, gridlines = false);





Download Roots.mw

The solve command also does the job here:

sol := solve(2^x+3^x+6^x-x^2);

allvalues(sol);


evalf(%):

The RealDomain:-solve command fails here.

I wonder how Maple solves it. It would be kind of Maple developers and experts to explain that.

PS. I tried printlevel:=10, but understood the output a little.

Edit: the commands sol, allvalues(sol), and evalf(%).