Jeez, I hope I never have to rely on any of the previous posters to do navigation for me. One left turn followed by one right turn will *not* leave you on the same _course_. It will probably leave you on the same *heading*, assuming both turns were of the same magnitude, but displaced some distance to the left of the original course. To get back to the original course, the pilot would have had to do the following:
1. Turn left by x degrees
2. After n minutes, turn right by 2x degrees
3. After n minutes, turn left by x degrees.
Anything other than that exact sequence of events* would have left the plane on a different course, so it's extremely unlikely the near-collision "would have happened anyway" - it is far more likely that by deviating from his original course, the pilot put his aircraft in the way of another plane that was sticking to its route.
At least this dickhead remembered to disengage the autopilot first, unlike that Russian guy who let his son turn the control column while the autopilot was on, which silently disengaged the ailerons from autopilot, causing the plane (an A320 IIRC) to plough into the ground.
* Of course, I'm not allowing for wind shear etc, but that's the point - course and heading are two completely different things - you can't just say that one left turn plus one right turn cancel each other out.