I don't think there's anything particularly magical about the number five. We weren't there and that may have been adequately deep analysis; we don't have the information to tell.
Personally, I can't say I'm inclined to think "the employee needs a table" is likely to have any useful root cause that goes any deeper... "I need a table" is hardly some sort of exotic need.
The whole episode is recounted from memory, not a transcript, so it's probably off a little. The real why answer is 'because he didn't have anywhere else to place objects in the work area'. The table is one solution. You could go another layer deep and wonder why the work area was designed without a stable horizontal work surface. Maybe the job duties changed, maybe the designers didn't know. At the fundamental level though, you've discovered a good corrective action.
Personally, I can't say I'm inclined to think "the employee needs a table" is likely to have any useful root cause that goes any deeper... "I need a table" is hardly some sort of exotic need.