Frame of brood donated to swarm. Lots of bees killed....

Last Friday I caught and hived a swarm, most likely from one of my hives. Saturday I took a frame of open brood out of a booming hive to place into the hive with the swarm. I have read that doing so will ensure that the swarm stays put. At any rate, I lightly tapped the frame of larvae and bees on the donor hive before putting it in a nuc for transport a few hundred yards away. I have placed a couple of nucs and the swarm that I caught on an old flatbed trailer that we no longer use. I didn't want the bees in the swarm to fight with the bees on the donor frame so I tapped the frame on the floor of the trailer hard enough to knock the bees off the frame. The bees started walking up to the front of the hive and fanning, just like a swarm would do.

I went out today to put a rock on the lid before the bad weather gets here tonight, and there were 100's of dead bees on the trailer floor, in front of the hive.

I'm wondering if I caused the nurse bees off the frame to be killed by dumping them in front of the hive, or would they likely have been killed anyway if I had just put the frame of brood, with them on it, into the hive.

Killing a couple hundred bees doesn't bother me, I just don't want to repeat the problem if I caused it.

I am wondering if the swarm, saw the bees that were walking into the hive as a rival swarm trying to overtake the hive?