First and as noted, the police are apparently confused. Second, it isn't the police who are trying to limit the rounds we can carry.
I know the police aren't. However, the argument is usually that they are pushing limiting the amount of rounds we have due to police being "outgunned" and also typically they go by information released by "police". Living in Florida I have the good feeling that every one of the Sheriffs within my fair state had stated they would not enforce laws that oppress our constitutional rights.
Sorry about saying they without stating what I meant by they. I know cops aren't gun grabbing. :P