Yeah, I agree after watching it some more it seems like he uses both his thumb and index finger.
I use this method for cr. Mk; very consistent for me:
D + mk~df~f~N + lk
Slight pause
Lp~mp/mp~hp/lp~mp~hp
There is a riddim to it. Just havta find it.
Edit: after spending some time in the lab tn on this, you don’t need to plink or anything. The timing on this after crmk is pretty easy. Tap down + mk, roll toward +k, quickly tap punch.