I don't know anything about the case in Uganda, but transfusion reactions can happen to anyone, even in the United States.

We don't actually express antibodies to antigens until we're exposed to them, so crossmatching won't detect a minor antigen mismatch until the first transfusion containing the antigen is administered.

That first time causes a delayed hemolytic transfusion reaction, which is generally milder than the kind of reaction crossmatching will prevent, but can be serious or even fatal.

https://en.wikipedia.org/wiki/Delayed_hemolytic_transfusion_...