This summary is not the rule. The rule text controls.
Here's a plain English summary of this rule:
If you need documents, records, or other physical items from someone who isn't directly involved in your lawsuit, you can still get them. This rule points to Rule 45, which covers subpoenas, as the tool you use to make this happen.
In practice, this means a business, government office, or individual who has no stake in the case can still be legally required to hand over paperwork or let someone inspect items they have. For example, if you're suing over a car accident, you might need medical records from a hospital or repair records from an auto shop. Neither is a party to your case, but you can still get their records through a subpoena.
The key takeaway is that being a "non-party" doesn't protect someone from having to share relevant documents or evidence. The court can still order them to cooperate, just through a different legal process than the one used for the actual parties in the lawsuit.