No, he draws a pixel with r=1,g=0,b=0,a=0. With a blend mode of ADD/ALPHA/INVERSE this would mean that r/g/b/a is multiplied with a first so everything is multiplied with 0 so it all gets 0. Nothing at all is drawn. With the blend mode he uses (ADD/ONE/ZERO) the r/g/b/a are simply copied (the destination is multiplied with 0, the source is multiplied with 1 therefore left as is). The alpha value (a=0) is not used at all.
The only unexpected thing is that when he reads the pixel back the alpha magically turned 1. This is a bug if the bitmap does have an alpha channel, otherwise is expected (a bitmap without alpha always behaves like a bitmap with an alpha channel of all 1).