I’m on the Silver Star #92, and conductor just made an announcement the train is “oversold” at Richmond. What does this mean? I know they closed the lounge to seat these passengers. Does it affect sleeper passengers?
Oversold means there are more passengers booked than seats available. The extra passengers are usually seated in the cafe and you may even have standees. It can happen for a number of reasons, although it's usually not planned. One common one is an earlier train being cancelled and Amtrak trying to accommodate as many people as possible. It shouldn't affect sleepers.
Speaking from experience, sometimes there will also be issues figuring out which seats are actually open when the train is right at capacity. Happened to me one time at ABQ when I was doing award sleeper RVR-ABQ, paid coach ABQ-FLG. I ended up happily plopping in the lounge and the conductor didn't force me to move when they did find the seats.
Amtrak will oversell by a limited amount, but as noted the fact that they have seating in the lounge car or can plop people in the seats in a spare sleeper room helps with this as well.