Well I totally called that one, but it was fairly obvious. I figure the events at the end of the last issue probably caused (at least part of) the problem. Chuck tore open his suit to presumably access his time travel device, so perhaps from wherever they ended up, (a) Chuck went back in time again to this point to warn Doc of what is going to happen. Since there is clearly some unstable time wormhole stuff going on, and Doc already saw his younger self, that could make this one of those "significant events" that you can more easily time travel to.
"I will not succumb to temptation, unless she's cute."