There are many parallel dimensions which we are not aware. We don't know about them because they are more secret than sekrit treaties. There is no entry to them until you have a special key which is holded by Parallel dimension Travelers. I suspect that Kev is one of them(he changed his name as a disguise but I found him and he is not hidding to call himself The Traveler). He's very likely brought The Johnsons to our world. We don't know their real purpose of being here but for sure we shouldn't underestimate them.
This happened in parallel dimension, is it our future?