Leave out the woulda/coulda/shoulda, okay?
The deal is that the shot did spread out so there wasn't a massive internal messup. After all, the doe was still wandering around, later on. The shot might not have been from as close up as the shooter thought, when he told the story.
Odds are that the choke wasn't Full or Turkey.
Bottom line is that buckshot isn't as effective on deer, for the average or novice hunter (and his shotgun) as folks believe. 00 Buck is what, 30 caliber? Coming out at only 1,200 or 1,300 ft/sec? There is a reason for all this R&D on slugs and slug guns for deer...
Art