Your snide remarks about "imagination" aside, the fact is that Beauregard didn't tell that to Anderson until the 7th, and communication with the fort was still continuing when Chew (not Lamon, thank you) showed up for his interview with Pickens and Beauregard on the 6th.
Chew was in transit from the 6th, as per my almanac, but arrived on the evening of the 8th, as per Nicolay.