I really don't think its a secret that the NRA keeps tabs on gun owners - they send them requests for $$$.
They can ask for any public records the same as you and me I guess.
And what do you think the NRA does with sign-up sheets for gun classes? Of course they are going to collect them and send out letters asking for money.
The NRA is a money making organization ~ that's what money making organizations do. Why would you think the NRA is any different?