Oversold flights can still sell seats sometimes if they are authorized to oversell by even more.

Zeroed out means that there are no more tickets left to be booked on the flight for a multitude of reasons. Could be it is 'sold out', which means that all authorized seats/tickets for that flight have been sold or it could mean that the flight no longer exists or is cancelled.

but if you are looking for a flight next week then there's a good chance it's just sold out.