As far as hearsay on the 2 deer. I saw that with my own eyes.
Now, that's different from your initial post of the story. If you had said, "I watched my friend ..." that would have been a conclusive eye-witness statement.
Given that you've seen two deer killed by buckshot and I've personally shot a number of pheasants, watched feathers fly, and then watched the dang birds fly away ... I'd say the verdict on birdshot as a large mammal/man killer is still a long ways out.