Yes, and if you read the account, the fort was in flames, and at one point in danger of it's magazine exploding. Sounds like that Southern Artillery was pretty good. Also, P.G.T. Beaureguard taught artillery at West Point, and was a former pupil of Robert Anderson. Even HE knew how good Southern Artillery was! Don't kid yourself. They could have pounded that fort out of existence.
It also doesn't sound like courtesy or gallantry, Southern or otherwise. More like a deliberate attempt at killing every man in the fort.