True in this case, but this isn't universal. Some devices with high voltage caps will absolutely still kill you even if they've been unplugged for days. This is why people can and do die while messing about with unplugged microwaves in particular.
This is true, but people handling those devices generally do protect themselves. In this case it wasn't necessary, so no need to stress!
Should be quite unlikely though. They are meant to have resistors to drain the caps. Can also short the cap with a screwdriver if you want to be extra sure.
People should not be messing with microwaves period.