AAMC Scored P/s #25

For this question, why does it say "Therefore, if sympathetic nervous system arousal had caused the differences, only the synchronous condition would have been affected." Based on the answer, shouldn't it instead say that therefore, BOTH conditions would have been affected?

Additionally, if the hypothesis is: "sympathetic nervous system activity is creating the conformity/obedience effect seen," wouldn't choice (C) reject the hypothesis outright?...

AAMC Scored P/s #25