I would guess that’s not a hard limit. Maybe they decided to undersell it because many 4TB+ nvme drives are physically larger and/or require heat sinks, so they might not fit. I don’t see any details on their web site though.
Given two drives with the same size, same heat output, and same interface, it shouldn’t make a difference.
It’s pretty common to see fake limits like that on spec sheets. I can definitely put more RAM in my motherboard than is officially supported since higher-capacity DIMMs are out in the same form factor now compared to when the mobo was released.