S1 is not satisfiable, and therefore the structure does not satisfy S1. The structure does however satisfy S2, since S2 is equivalent to [(Fb) WB (Fb)], and Fb is always false since f is always false on the single path the structure has. Note that [a WB b] holds if either (1) a holds before b holds or (2) we always have !a&!b (which is the case here). So, you are right, the second sentence should say that the second formula is satisfied.