Question was "Are we alone?"
Q answered "No." (WRWY) ←just sayin'… could mean almost anything.
Next Question was "Roswell?"
Q answered "Highest classification (what goes on there is of the highest classification).
Then said "Consider the vastness of space." (What highestest classification stuff would require all that land/space in Roswell/Area 51?) Implication may have been that figuring out what Roswell is al about can be more easily narrowed by determining why they need so much (vast) space sealed off.
See how what Q said COULD be interpretted?