But you sound more in the now about their internal processes, so you’re probably right and I misinterpreted what they meant by that quote.

The general summary of how "bugs" work in software development is simple at a high level.

1. Someone reports the bug (developer, qa, player, user, etc)
2. Someone prioritizes the bug
3. Lower priority issues are put on a backlog to potentially be worked on later
4. Higher priority issues get fixed (most of the time)

The product releases when an acceptable level of bugs from steps 3 and 4 are reached, and "acceptable" never means zero or even close to it.

So, the developers have a pretty good idea of how many bugs there are, in addition to the more general sentiment that the people testing have about the stability of the game.