Some thoughts about your questions.
I guess "the races" is best thought of as a competition involving animals or cars. A race involving people as competitors is normally called a "track meet." Still, given a specific context you might call an event involving people "a race."
In general if you are competing you would say "I was in a race," if you are a spectator you would say "I was at a race."
I don't think I would ever say of a track meet that I had attended "the races."
"the races" can be any racing event not involving people as competitors (horses, dogs, cars, etc.) the context will tell you which.