Streetpass is confusing me

So I was traveling a lot recently, and all these people showed up in my plaza, but they didn't show up at the gate. I cant use them in games or anything, so I am confused as to what they are even there for.

So I was traveling a lot recently, and all these people showed up in my plaza, but they didn't show up at the gate. I cant use them in games or anything, so I am confused as to what they are even there for.