Looks fine to me. Some creatures have multiple creature weapons, some creatures have some that do dual types, and I suspect your "damage reduction wasnt respected" because at the time you had a greater damage reduction already from greater stoneskin (you absorbed 20 points), damage reduction doesn't stack with damage reduction, it just takes the highest that works for the situation.
Which is why Huge Shabaoth was "playing fair", because it can hit past your greater stoneskin (because it doesn't play fair, lol) so your barbarian damage reduction has the priority.