Manual Hubs front differential question

Hello. I’m working on bringing a 99 with manual hubs back to life and have a question about the front differential. The drivers side hub is working well and free but the passenger side hub is stuck in the locked position. No big deal, I have a kit and plan to rebuild both hubs. What concerned me is I was working under the truck yesterday with all the wheels on the ground and realized I could spin the front driveshaft freely and it would in turn rotate the driver side axle without turning the passenger side. With the wheels on the ground and the passenger side locked I did not expect to be able to turn the front driveshaft and diff. Does this mean my diff is blown up or is it designed to somehow magically work that way?

 

Open differentials look for the easiest path of power, which is the drivers axle. This is normal.

 

I don’t know what wizardry is at work inside that metal orb but this is the answer I was hoping for. Thanks!