It was a MiG-21bis. Which is nowhere close to a 4th gen standard, at best, its a 3rd gen standard. My point is simple - if a MiG-21bis can take down a plane an entire generation superior to it, the conventional planes Russia has wont have much problems with the latest gen F16s.
For your info, the MiG-21 in service with India is of the Bison standards, it is the most advanced version of the MiG-21, it is fitted with various goodies, BVR missiles like R-77, Israeli jammer pods to name a few so I would not call it a 3rd generation, neither maybe it could be called as even close to a fourth generation plane either, we can say it is between meaning it is a near 3.5 gen fighter.
But yes, the MiG-21 is indeed much behind the F-16 when it comes to technological sphere, the reason WC. Abhinandan managed to down the F-16 by firing an R-73 was cause of the fact that the F-16 pilots were not upto the mark. A while back, there were some sources citing how Pakistani pilots were given just passing marks in F-16 training, no wonder they lost a prized falcon to a mig.