I think he meant that with Qa2b3 that there could potentially be up to three other queens, precisely because you should only provide the minimal disambiguation.

• If Qb3 is insufficient,
  there must be another queen that can move on b3.
• If Qab3 is insufficient,
  there must be another queen in column a that can move on b3.
• If Q2b3 is insufficient,
  there must be another queen in rank 2 that can move on b3.
• Since both Qab3 and Q2b3 are insufficient, the board must be crawling with queens poised to attack b3.

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