this is very much not a case of, "Eat a mosquito, get a gene". Eating, no. But it's my understanding that while uncommon, it does happen that viruses transmit

this is very much not a case of, "Eat a mosquito, get a gene". Eating, no. But it's my understanding that while uncommon, it does happen that viruses transmit genes from host organisms. Since the virus is hijacking the host cell's reproductive equipment, and all that DNA is just hanging around there, it's easy for some host DNA to get incorporated into the next generation of virus. (Conversely, I believe that one theory for the origin of "junk" DNA in our genome is that it's viral genetic material accidentally incorporated into the host genome.)