Question

is double displacement reaction a redox reaction

Answer 1

NO, double displacement reaction is not a redox reaction.
Since there is no simultaneous oxidation and reduction the the chemical reaction.
Ex:(i)NaF + KCl >> NaCl + KF 
     (ii)AgNO3 + NaCl → AgCl + NaNO3
     (iii)CaCl2 (aq) + 2 AgNO3 (aq) --> Ca(NO3)2 (aq) + 2 AgCl (s) 
Hope your doubt was cleared.....comment if doubt persists....!!! :)

Answer 2

yes the  double displacement reaction a redox reaction
In displacement reactions, one or more atoms is swapped out for another. 

AB+C→A+CB