If it's an established hive, you haven't moved it and nothings changed other than them swarming then i would say it's not an orientation flight (sorry yanta). The bees have no need to re-orient and you won't have sufficient brood moving across to field bees on that exact day to explain what you saw. Also, prior to swarming the previous queen would have stopped laying for a bit so i wouldn't expect massive numbers of young bees in your hive. Is there a laying queen in there now and are there any other queen cells? The dead give away for me is the fact they're building comb under the lid - they're full and need more space. What i personally would suggest doing, and others may present alternative ideas, is free up some space in the brood nest - put in some undrawn foundation - if it's warm and population is booming (which it sounds like it is) you could get away going F-B-F-B-F-B-F-B with F being undrawn foundation and B being brood in the brood box. Then i would move some of your capped honey in your ideals up in to the top box and replace that with some of the undrawn foundation that would be in the top box - this will give them more space but also encourage them to start working the top box. This is one situation where i like to have consistent box sizes - if they were all consistent you could easily move some of the brood frames up in to the top boxes - this would allow you to put more space in the brood nest whilst also allowing the capped brood in the frames you've moved in to the top boxes to hatch and then be backfilled with nectar