The 1 point safety (Tex A&M did this last year) for A doesn't answer the OP's question, as it is exactly the same as a regular XP - 1 point for the offense.
I think the OP was asking how a team could have just 1 point - total.
The same rule, however, gives the only option. A scores, B blocks XP, and A ends with the ball in their OWN EZ (long run by B plus a fumble, with A running the ball into their own EZ, for example). B would score 1 point on such a play, and the score would be 6-1.