Viral infection can sometimes turn into baterial infection too.

If a fever lasts for a week with spikes of 102, it's almost for sure more than just viral. Doctor probably have antibiotics based on 1 - persistent fever and 2 - highly likely he heard something in the lungs. And the fact your little one responded to antibiotics the very next day proved that antibiotics is necessary. Don't worry much about the use of antibiotics once in a while. In this case, it does more good than harm.