To be able to move smallpox simply means to have a device within a writing ink pen that could very easily pass any customs officer, could easily pass through a metal detector, and you could have enough smallpox in there to start the world's worst epidemic.
That means that very, very limited supply is going to become a lot more limited.
While the numbers in the study are very small, the resistance and clinical failures here are very important. Resistance could mean the difference between surviving and not surviving.
There clearly have been ongoing changes in the virus itself, and what that means in terms of its adapting to different bird species or its ability to infect other bird species is unclear, but it may have played a role.