Same scene, completely different interpretation.
Here is what IS known: A small part of the 11th New York and all of Reynold's Marines, who were to the left of Ricketts's Battery on Henry Hill, were fired on by Arthur Cumming's 33rd Virginia. The fire was sudden and intense, and the Marines broke ranks and fled back down Henry Hill, followed by the Zouaves. They ran to the Sudley Road cut for protection.
There was no protection to be had. Just as the Marines and the men of the 11th NY reached the cut, 150 mounted Confederates, under the command of JEB Stuart, reached the road as well. The Zouaves initially managed to establish a firing line and got off at least one shot, referred to as a "sheet of flame" in some sources.
What happened next was terrible. According to Edwin Barrett and W. W. Blackford, both members of Stuart's Cavalry:
I could see horses rearing, sabres glistening, and revolvers flashing. . . . I leaned down in the saddle, rammed the muzzle of my carbine into the stomach of my man and pulled the trigger . . . blowing a hole as big as my arm clear through him."
The "pet lambs" were indeed slaughtered.