Where did you find this info? The article says it was Tesla that did a voluntary recall. The NHTSA was not the one who did any testing and was not involved in the decision. The report, which is linked in the article is authored by Tesla with no involvement from NHTSA.
If I am misinterpreting something I thank you in advance for pointing it out.
- On January 25, 2023 [..] NHTSA advised Tesla that it had identified potential concerns related to certain operational characteristics of FSD Beta in four specific roadway environments [..] NHTSA requested that Tesla address these concerns by filing a recall notice.
- In the following days, NHTSA and Tesla met numerous times to discuss the Agency’s concerns and Tesla’s proposed over-the-air (“OTA”) improvements in response.
- On February 7, 2023, while not concurring with the agency’s analysis, Tesla decided to administer a voluntary recall out of an abundance of caution
So yes, it was voluntary in the sense of "you don't want us to force you to do it" and it was indeed the NHTSA testing.
This recall only happened because, god forbid, the NHTSA got off its ass and actually tested something.