The big difference was that he was going for a full length portrait and I was doing a "head shot". He was 25 - 30' away from he's subject. I was less than 10'. He was shooting at 200 mm, I was shooting at 270 mm. He was at F 2.8, I was at F 5.6. A full two stops closed down from what he was using. This guy shoots weddings. Again ???
Let's go to another friend. She had just gotten her first DSLR. She had been using a Canon G11. If you're going to shoot with a "point & shoot", Canon's G series has been the high end since they came out their G series. So, she had had a pretty darn good camera that she came up from. She said she'd been working her way through shooting in manual and changing only shutter speeds to see the effect the shutter speeds had on her photography. Her next step was going to be changing only the F-stops to get an idea what they did. Interesting experiments. Once she finishes her testing I hope she will translate that into using Aperture Priority and know what's going to happen with the F-stop she selects. I told her she had bought a thousand dollar plus computer. (She said she was still using her old computer and she'd bought a new camera. I let her know that she had bought a single purpose computer that people referred to as a camera.) I asked her not to use it as a glorified shoebox. I recommended she make all the decisions and let the computer (camera) do all the math. I'm a big believer in understanding what you want in an image, making the decisions necessary to make that image and letting the equipment do the heavy lifting.
Take a look at today's image. What do you see as a background? It's the side of a school building with the brick texture stood vertically. Look again. You might be able to get a faint idea of what's there. Selecting the F-stop isn't the only factor in throwing the background out of focus. Understanding what the camera will do is important.