What happens if someone doesn't turn up?

Every match has a deadline. If no result has been reported by then, the match is closed automatically and the seeded side advances — the bracket shows this as Advanced by default or a Walkover rather than as a played result.

That is why not turning up is worse than withdrawing: the round moves on without you and your opponent goes through.

If you were present and the match still closed this way, tell us which tournament, which round and roughly when — that is enough for us to look at what the game reported.