It is Bootcamp (repartitioning and dual booting to a second OS other than OSX), and yes, you can do that. It works really well.
"Go Mac because it's faster" is not really the best reason, since your game, even in Bootcamp, will probably not run as fast as a Windows machine at the same price. What your friend said offers no real insight as to why. Macs use the same Intel processors as Window machines.
As someone who came from the Windows world into the OSX world, I can say that, side by side, OSX and Mac does not game as well as Windows. Processing a single photo is not going to show much difference in speed. Lets be realistic.
Now, the difference is in the raw power of the full 64-bot OS with 64-bit apps. I notice the difference when I am processing video. FCP vs Sony Vegas Pro (11) there is no contest. When I was Bootcamped and running Vegas, a 5 minute short done in 4k took 30 minutes to process and render a simple filter (8mm + Color Correction) and compression to 1080i. In Final Cut Pro X, the same process took slightly more 5 minutes.
Again, will you notice a single photo difference in speed - I haven't. I still bought the Mac, however, and I use it for everything. I have, in the last 2 weeks, been able to get rid of my Bootcamp partition and go back to OSX completely. No more dual booting.