It suggests to me some kind of susceptibility on the part of the receiver, whether the virulence of the contact or something within their own makeup that is more prone to infection by this virus or something about the method of entry by the virus.
There are probably humans that are immune. Dogs, for instance, are known to be mostly immune, despite being susceptible to infection.
But the most likely hypothesis for humans is that the volume of the exposure matters. I.e., it's more dangerous to handle an almost-dead patient than to be in the same apartment with a new patient in the process of getting sick enough to be hospitalized.