If these are both "relative to baseline" and not "relative to one another," then yes (except for spelling and grammatical mistakes).
Of course, as stated, not taking a nap apparently gives a greater improvement, so presumably they didn't actually mean "decrease" and instead meant "increase."
Baseline would be the test that you performed prior to the flight.
Take 100 pilots. Test them all right before flying. Instruct 50 to nap during the flight. Instruct 50 not to. Compare each individual's response time after the flight to their response time before the flight. Aggregate by group. Perform a t-test (or another appropriate test) asking whether or not the difference (after minus before) is the same in both groups, or if one group performs better.
Of course, as stated, not taking a nap apparently gives a greater improvement, so presumably they didn't actually mean "decrease" and instead meant "increase."