I’m sure you’re reported this accurately, but I think there might be a semantic problem. The Open’s policy is that it’s an outdoor tournament.
https://www.usopen.org/amp/en_US/ne.../rules_of_the_roof_when_to_close_and_why.html
This changed last year:
The rising heat and humidity at the U.S. Open has prompted organizers to adopt a new policy that allows them to partially close the roofs on the main stadiums.
apnews.com
I’d be surprised if they’d suddenly started closing the roof for heat. I think they may have adjusted the placement of the roof to add shade, without fully closing it.
EDIT: That’s what they did. Closed it part-way for shade. Quote from Aetna: “
On the conditions: "A half-closed roof definitely helped a lot. When I came out onto the court I was saying 'thanks' to the person who did it because this is really helpful.”