Does a decrease in frc always mean restrictive lung disease? I am not obese. & my fvc was 95% of predicted fev1 was 96% fev1/fvc is 81% w/significant improve. W/bronchodilator, why was frc decreased?

Results are normal. There is a normal range for every test. It could be defined in different fashion & it varies wig test. Normal people could be in 80 to 120% range. More scientifically speaking a normal range should include about 90% of normal people.Your results are in normal range. Reduced FRC does not always mean restrictive lung disease. It could be related to technique.
Nonspecific. Reduced FRC can be reduced from a few things including posture or very good fev1 (like yours being 96%). However, if you did have significant improvement post bronchodilator you could have small airways issue like we see with allergies. Does not mean ild/restrictive changes all the time. It would be more likely to be significant if tlc/vc was reduced.