i think the killer is just that, he doesn't need a big reason in choosing a victim, he just fixates on someone until he get his way (killing them). I think that Sol just happened to be in the wrong place and time in both the original timeline and this new timeline (both times she got out of the bus at the reservoir and even though it on different dates, it's still the killer's preferred place at that time). on the original timeline she got kidnapped right away but in the new one the killer must have taken the opportunity of kidnapping her when Sol's grandma voluntarily gave their home address, making it easier to fixate on her again. on later episodes i think it becomes clearer that it doesn't matter who the person is as long as he's locked into it already.