Why would a foreign power want the victims to bring along things that could be tracked or would be traceable?
Exactly. They wouldnt which means this group knew in advance, they arent abductees. They left behind things like keys, wallets, phones, wrist watches, etc. You dont do that without a purpose. Some with bags, the general remembered to take his pistol but nearly nothing else. They are runaways, whether they went into a program to hide them or something like that we may never know. Did they all leave home to go into hiding because they were warned there was plot to kill them? Did they have to leave knowing that there was a plan to abduct them and disrupt their research. We cant know yet but at least 4 got away, whether from “the Chinese” or “little greys” is irrelevant.
If you left your house for a walk tomorrow at 8AM and the little grey chinese teleported you into their windowless van then you would have your keys, watch, phone, pocket knife, and whatever else you normally carry. They would have to decide what to do with it so that you werent tracked.
The only reason to leave everything behind is because you knew in advance that you couldnt allow yourself to be tracked when you left.