In real time yesterday (albeit from my seat at the other end of the ground) it didn’t look like a pen because of the obvious change of direction of the ball when Naismith made the tackle. Looking at the footage, VAR might have given it, but as @Davefevs has pointed out, that would have been contrary to the way the game had been reffed (and I thought overall the ref was good yesterday).
I really don’t like the way VAR can over-complicate things to the extent where these grey areas occur. There are justifiable reasons for arguing that a penalty should have been given. But in real time it looked like a good tackle, Naismith got the ball and the ref’s decision to not give the penalty was sound in my opinion.