Logan forced the man into helping him remove the mountain ash surrounding the building before knocking him out and keeping him aside. He tied him up just to be on the safer side.
With the mountain ash destroyed, he could infiltrate the hideout whenever he wanted, but he decided to wait a little longer since he didn't want to rush into the hands of the hunters. There was no guarantee that the old man hadn't informed them of his plans in some way or the way. And he knew for a fact that they would be able of what he did to Daphne with the Banshee.
Logan would've been affected by it as well, but since Logan seemed to have developed some sort of resistance to these things, only Daphne was affected by it.
The man guessed Logan was immune to these things, and seeing him come for him showed this.
