a) animals (including humans) that have antibodies but have probably cleared enough of the virus to be no longer infectious, i.e., they may have small amounts of the virus but not enough to transmit;
b) animals (including humans) that are fighting off the virus successfully (and so have no or few symptoms) but who carry an infectious level of the virus;
c) animals (including humans) that are not fighting off the virus successfully (initial stages) but who show no or few symptoms yet but who carry an infectious level of the virus;
The fact that there is no direct proof of transmission from dogs is meaningless (there's no direct proof of transmission from bush meat either: by the time an outbreak is detected, the meat and carcass are long gone).
The question is: can an asymptomatic dog carry enough live virus to serve as a transmission vector? We probably don't have enough knowledge to make that judgment, but based on the disease and other animal cases it certainly seems possible.
Don't get me wrong: I feel sorry for the dog, but I don't see any reasonable alternative to putting it down and cremating the remains.
I suggest you return to the article that is the topic of this thread and read it. The dog has not been tested. They have no clue as to whether it was infected or not, they’re just going to kill it.
And even if there are antibodies present, there is no evidence in any literature anywhere that dogs can infect human beings.
By the way, there are near riots outside that apartment in Spain. People are trying to prevent the dog from being taken and killed.