Some people are using presymptomatic and asymptomatic interchangeably. I suppose this distinction might be useful:
- Someone who is asymptomatic has the infection but no symptoms and will not develop them later.
- Someone who is pre-symptomatic has the infection but don't have any symptoms yet.
Feel free to bring more learned definitions to the terms.
If I am pre-symptomatic--I still have the virus and I may be shedding it, while showing no symptoms.
In your example above there were pre-symptomatic people at the party, NOT symptomatic people. The example is of people who were displaying no symptoms at the time.