“0 iterations” means that the solve did finish successfully, but it was able to find an optimal solution without doing any iterations of the chosen algorithm.
I confirmed this with the Gurobi solver, and after solving, the AMPL command display x, y; showed that the optimal values of all the variables were zero! In fact it is easy to see that 0 is the smallest possible value of the objective function; and also when all of the variables are zero, the constraints are all satisfied. For a trivial optimum like this, it is not so surprising that no iterations are needed to find the solution.
When an unexpected solution like this appears, it is usually due to a simple error in one of the constraints.