The guy is probably proud of his prog, that's why he published it. Indeed, that's more a C approach than a C++, but anyway for solving a sudoku there is no need to put in place a lot of complex data structures.
What I like in this prog is that he optimizes the process by simply considering that since any 1-9 digit can only be once in each column, each row, and each of the nine 3×3 sub-grids, he uses a 10 bits int and associate 2^i with a digit (instead of an array, or worse checking all digits each time). Then 'Place()' recursively tries only possible combinations which converges quickly to a solution.
Good prog. I wish all political figures would be able to show such an artwork!