This is meaningless without knowing how productivity is being measured. It's very possible that said metric inherently favors in-person collaboration over remote collaboration - which would then skew the results of any further analysis of that metric.
This is also meaningless without knowing exactly what's being compared. I wouldn't be surprised if 3 in-person days a week was indeed more productive than 0, but what about 2? 1? 1/2? 1/30? 1/365.24? There's a lot of numbers between 0 and 3, and coming to any conclusions without understanding the actual shape of that graph is folly.
This is also meaningless without information on the wide range of in-person cultures or the wide range of remote cultures. These preliminary results could readily come about from having a remote culture that's more dysfunctional than other remote cultures and/or an in-person culture that's less dysfunctional than other in-person cultures. I've personally experienced both ranges more-or-less in full over the course of my career - as well as varying combinations of the two in hybrid environments.