My thought is that they came from different production batches and the shipping warehouse pulled inventory on a first-in first-out basis. Evidently, there was one left from the earlier batch. At the moment I don’t think that inventory sits around very long. You could check the serial numbers. Included as the first few characters is the manufacturing date code. I’d be surprised if they were more than a few weeks old. It’s also possible that the inner cartons came from different batches. or suppliers and that the units are from the same production batch. 

I assume that you recently purchased a pair. If I was the shipper, I would try to avoid situations like this. Unfortunately, there is no way to know which inner carton is inside the outer carton. If you purchased these units from a large volume shipper, the packing agent is under heavy stress to pack as fast as possible and would not have time to check details such as this. SONOS is constantly fussing with the packaging. 

The box on the right is the new eco-friendly packaging by Sonos. It’s part of their sustainability initiative.

Packaging with care

A comprehensive approach to product circularity must include packaging. In FY21, we undertook a significant update to our packaging design to better align with our sustainability objectives. The solution uses Forest Stewardship Council (FSC) certified kraft paper and was first introduced with the launch of Sonos Roam. By FY25, we aim to use 100% post-consumer, FSC-certified, and recycled plant-based fiber paper.

https://sustainability.sonos.com/Product-Sustainability/default.aspx 

I wouldn’t worry too much about it. The speakers are the same. One just has newer packaging.