My opinion having done this job a few times.
1) I can't see how a buffing wheel would have been used. It would have been really hard to get the wheel to the end of the flat without rounding the serrations in the slide.
2) There are really only 2 right ways to do this job, only one of which will work if the serration tips are up level with the flats, those are:
a) With emery paper backed by a hard flat tool
b) with a surface grinder (only workable if the serrations are recessed a little).
Most shops don't have the required magnetic chuck and surface grinder to do it that way, and frankly, the setup would be a lot of work. draw-sanding the slide would be faster and probably more profitable if the gunsmith has skill.
You get rounded edges like that when the sanding was done with a soft backer, like a foam sanding block, or if the paper was not tightly wrapped around the backer. With the degree of rounding on the corners, I'd bet on a foam sanding block being used - which is totally amateur hour. The only really valid use of foam blocks are when doing compound curves, like when you finish sand a wood stock at very fine grit.
That's my $.02 worth.