It makes just as much sense as any one of us being from another time. The fourth dimension, which governs time? It's like a ribbon with one end being your birth and one end being your death and every other moment inbetween.

Which means that's the dimension which is under flux right now and it's distorting the space around us.

As for why you're here? Any one we know, it makes sense, since you all have connections to someone aboard the wave rider.

Not sure about Bart or the other kid.