W1slicer it's a butterfly effect sort of concept. The idea is that because the past changed in a minuscule way, things happened slightly differently and changed the present to some extend. Think of the ending of back to the future, where everybody is slightly different. Johnny may have been conceived with a different sperm cell in the new timeline. Doesn't make complete sense, obviously, but that's because time travel can never make perfect sense, you always accept some level of timey whimey wibbly wobbly. :P