Anytime you involve any sort of time travel in a show everything gets wonky lol. I think akkun came to that conclusion though because realistically if someone gets pushed on to some train tracks, no one would really notice until it's too late especially considering how close and fast the train was. Hell even if you see someone looking like they're about to push someone I don't think most people could react that fast. So even though it sounds crazy, the only logical conclusion would be someone had the knowledge already.