Thanks for trying it out!! Yes the new towers are placed randomly, with the gun turret pointed toward your mouse. He said he uses a random value for x and y for each tower (and he isn't sure why they always appear in the top half of the screen - maybe bug or maybe feature:)
Since he is already using the mouse to aim the bullets, I was expecting that the new tower appears wherever the mouse is. It looks easy to implement. (I always say: That's easy and it will take me 10 minutes. But it always take much more time, like 3 or 4 hours :) .) (It also will be nice to center the new tower under the mouse. Add another hour of development.)