If the second swarm had a queen and she was laying eggs, pharmones were stronger, it is a possibility that the first swarm did move out and join up. You see that with packaged bees when several are put into hives in the same area. The queen with the strongest pharmones ends up with all the straglers and some of the workers from other hives. I had 1 out of 10 packages do me that way this year. Good thing was that it didn't hurt the hive too much and after she got to laying they went wild.