Aren't fouls during a punt enforced from the line of scrimmage? Exception: Illegal touching, fair-catch interference, invalid fair-catch signal, or personal foul (blocking after a fair-catch signal).
(From online rules) Everything you're saying is correct - but from the one reply that I saw, it seemed rather obvious the Panther player pushed the 'Skins player right into the 'Skins punt returner. I would have thought that would negate the fumble. But maybe I'm wrong. I know that in the NFL, if player A shoves Player B into Team B's goalie at the point where the puck is being shot into Team B's goal, the goal is disallowed (and a penalty against Team B).
However, I didn't see the Redskins arguing with the replay, so maybe I'm wrong. Every week, the head of NFL officiating appears on the NFL network and they talk about controversial calls, so I wonder if they'll talk about that one.
But anyway, congrats!