Walter's Weird Night<br>Walter noticed something strange in the sky one night. He didn't believe in space aliens, but he was confused. He was sure he had seen a flying saucer in the night sky. Then he saw on the news that a weather balloon had crashed. Walter was relieved that aliens hadn't come visiting after all.
Walter saw a weather balloon in the sky one night
The context only says that a weather balloon had crashed, not that it was what Walter had saw. It might have crashed in a different place. He might have actually seen aliens. The system has likely made the jump in logic that the thing Walter saw was the balloon. 
( z1 see :ARG0 ( z2 person :name ( z3 name :op "Walter" ) ) :ARG1 ( z4 balloon :mod ( z5 weather ) ) :location ( z6 sky ) :time ( z7 date-entity :dxyperiod ( z8 night ) :mod ( z9 one ) ) )