Sims trespassing in Sulani

I just moved a couple to Ohan'lani (or something like that) town, into the lot next to that temple looking place. Called Tangled Flat, I believe. As always I gave it the private dwelling trait, because I can't stand random sims showing up on my lots. And I always lock the doors to everyone but household members. So I was shocked when that evening a child came up on to their deck & started playing chess. My sim chased him off, but no sooner had he gone then two more children showed up. They've been standing their talking on the porch for some time now.

https://i.imgur.com/unSHVg6.png

And now I spotted this toddler talking to one of the household members.

https://i.imgur.com/M9DvL0Y.png

The toddler is from another one of my households, but the boys are NPCs. So what gives here? Is there something about this neighborhood, or is it a bug, or is the lot trait no longer working? It hasn't been a problem in any of the other lots I play. The toddler I don't mind so much, because she's one of mine & actually socializing with a household member, but I'm an anti-social control freak who doesn't want random sims just hanging around on my lots uninvited.

Edit-they left a few minutes after I posted this & no one's dropped in since (about 1 1/2 sim days), so maybe it was just a momentary quirk.