What happened was that when i talked to Preston to get the bomb thing, I was too soon and got him to follow me. That has happened before aswell, so its not a big deal. But of course, this time it decided that Preston would not give me the dialogue and let me continue the run :( Watch out for this when you're running, wait for Preston to talk to you or something.

I think this happened to all of us when we started running :P

Not to me cause you taught me how to do it correctly Havrd-sensei !