Since Williams defines the very bottom of the race grid, they don't have much to hide in terms of technology. So releasing a 3D model of their car in this form is nothing that would harm the team at this time.

It is possible that their aerodynamics are good or even best of all F1, while the motor, the suspension, the tires, etc lag enough to nullify this advantage.

Williams engine is supplied by Mercedes, tires are shared from Pirelli. But sure there are other parameters as well apart from aerodynamics.

Do you know any more details about the leak? The article didn't really discuss it.

The regs are changing anyway so the risk is basically zero even if they had something worth stealing.