Looks like probably that chart is just somebody's copy/paste error. Here's "widths measured across the rivet" from ParkTool:

• 12 rear cogs — 5.3 mm
• 11 rear cogs — 5.5 mm
• 10 rear cogs — 6 mm
• 9 rear cogs — 6.5 to 7 mm
• 6, 7, and 8 rear cogs — 7 mm