Your friend might have wired in different Omron switches with different poundages...lighter I would assume, but that would be my guess. Unfortunately, the only reason I know about all these switches is JLFs and Sanwa Beatmania buttons. Louder = better.
I like it loud. Even my buttons are loud. People say it's scary when I bang on all four buttons for a CF, because the springs in my button cylinders make a faint ringing noise, and they kind of harmonize when you hit four at once.