It does sound like this may have been roseola. As you probably know from the research you have done, roseola is a very common viral infection in infants and toddlers which usually begins with a high fever
then followed by a typical splotchy rash. Very characteristically, the fever goes away usually several days before the rash does. So it sounds like your son is right on track here!
It is always a good idea to have any acute illness evaluated by your pediatrician
. This is because, even in cases that seem relatively straight forward, it is always possible that your son's symptoms are due to another condition that would require more aggressive medical treatment. Your pediatrician will be able to confirm the diagnosis of roseola or make an alternative diagnosis.
If this does turn out to be roseola, it, like any viral infection, is contagious and it can be passed in respiratory secretions (saliva). Typically, the infection is acquired in infancy or childhood, and it is mostly children who pass the virus back and forth to each other. After a child has the virus, they tend to be immune. Therefore, you yourself are probably already immune to roseola. Nevertheless, if you have any symptoms at all, you should also go see your primary care doctor