The Man in the High Castle knew that obviously that tape did not depict the timeline we are watching and therefore was not showing San Francisco within that timeline being destroyed. That tape must have come from another alternate universe, where it did get destroyed at some point in the past.
It seems as though he was trying to work out WHY in that universe, San Francisco was not bombed.
BUT that sort of doesn't work, as otherwise we aren't talking about just people leaping between parallel universes, but also time travelling... (if we are to believe that tape shows San Francisco being bombed due to events we see unfolding in the second season.)
So the main question, was the San Francisco tape just a red herring (ie not a tape from the future) - ie a tape to make Juliana believe that is what was going to happen in her timeline, when in fact it was just a video from a random alternate timeline.
The Man in the High Castle perhaps knew this, but also knew war with Germany and Japan was coming and that perhaps only Juliana could save it in this timeline we are watching.
Basically, there is no way that tape showing a nuked San Francisco could be from their own timeline, unless people are able to time travel within their own timelines as well...
I don't have much more to say but if you're on the fence about giving it a go then try it.
