Hope his daughter is not in critical condition. We are seeing more and more cases of young adults/teenager being hospitalized over COVID. Some had no previous condition.
The previous condition/comorbidity thing can make things much, much worse, but it's not the only reason some people get hit really hard. In some cases, peoples' immune systems basically lose their shit and go HAM (these are the technical terms
). Capillaries in the area of the infection already open up a little bit to allow white cells through to fight the virus. Inflammation lowers the lung volume a bit on its own, and dead cells from the infection (both lung cells and white cells, and mucus) start to fill the lung with fluid, further reducing capacity. When things go off the rails, the immune system really opens up the capillaries and intensifies its attack, and also starts attacking any target in the area, not just the virus (this is called a cytokine storm). So now you have a much greater amount of inflammation, a much great rate of fluid accumulation, and the body is attacking healthy tissue. And add a high fever on top of this. And as far as I'm aware, there's no way to predict who may react in this way (it's not age dependent).
It sounds like splitting hairs, but it's not so much that the disease is really bad in some people, it's that some people's immune systems react REALLY badly to this infection.