You don't know for a fact that the bees did survive, you only know that the hive is active. They could as easily have died and then been inhabited by a swarm from someone elses managed hives.

No, these bees never died off.

I think Bamboo makes a good point. They could have died off, unless you went out and saw bees there every day. Every day.

However, they may the original survivors too. Maybe you have superior stock.

Swarming tends to break the brood cycle, breaking the brood cycle also helps deplete varroa mites.
That coupled with some favorable conditions might be the reason they survived if in fact they are the continuation of the original colony.

My friend's hive didn't make it through this past winter, but there are already new bees that decided to take over the hive. It happens so fast sometimes. It is possible that it is the original colony, but it is also possible that it isn't. Unless you check the hive often you can't be sure either way. In that amount of time it is possible for the hive to have had a few different colonies. Who knows?