At magnification ratio of close to 1:1, such background blur is easily achieved especially when the aperture (that on the lens, not actual) wide open to f8. This is regardless if you use extension tubes or diopters. However, if you use diopters, the wide open aperture remains the same as your lens. If you use extension tubes, your wide open aperture will be closed down. It helps much if the background is far away and softly lit.
I am very impressed not by the background blur but by the beautiful "bokeh" achieved. I am not familiar with Canon lenses but I had never seen such beautiful "bokeh" from my Nikon lenses. He may also had applied selective unsharp mask to the flower and not to the background which really makes his flower shots stand out.