His calmness and everything is mostly to do with him being an adult who had a decent education, but not specifically about him having medical knowledge. Ruby's a kid who had an illness that meant she stayed in a hospital all day watching videos.

Aqua could have been an engineer, banker or a programmer at a firm prior to dying and it wouldn't have made a difference so far. Being an adult with a prior education helped Aqua. People skills in medical professionals are a bit of a hit or miss, even though we're technically taught it. (Even then it's basically "Listen to people" and "be empathetic")