I've got four children of my own, and raised more than a few, including my younger siblings when my father died and my mother went mad.
All in all, it's pretty good advice. Don't stress on what your son is doing, he's reclaiming the excitement he felt watching it, it's good excersize and imagination is vital to a healthy child.
HOWEVER...
Do NOT hide or conceal the swords. He already knows they exist, and by hiding them, they become "forbidden fruit" and "something neat that Daddy is hiding from me" and THAT can cause trouble.
Instead, do something simple...
Take one of them, cut a watermelon in half, and let your son know that they are dangerous for people to play with, that it can do that to someone by accident just as easily. Put them somewhere "on display", preferably a weapons case that locks, so he can look at them and imagine, but not get at them easily.
While my weapons locker is on the back porch, it is locked and secure, and I've never had problems with my children trying to get into it. (Of course, they're also trigger locked with the bolt removed, ammunition removed, and locked down, but that's different)
Allow him to act out his fantasies, and if he wants a sword of his own bad enough, buy him a plastic one and allow him only to hit a specified object.
But if you hide them, trouble will follow...