I'd tread lightly, questioning another growers knowledge.

After all, YOU just asked a beginner question about topping.

HOWEVER, instead of a demeaning comment, you got an answer from me.

And, you got ADDITIONAL advice, from one of the best growers on here.

Take that advice, say "Thank you" and drive on. 

There's no need to be disrespectful.

We're all here to help one another.