The ammo confiscation appears to come from an undefined Restraining Order banning him from “the purchase of ammunition”. I however, would believe that the headline dealing with ammunition was more likely to sell newspapers than “Man Violates Restraining Order by Making Retail Purchase”. Recognizing that bias and having looked at the source story (a real hatchet job against the man); I would tend to believe that the police may have acted rationally, but the story would have been quite different and would have lacked the panache.
No, the RO need only exist. The Lautenberg Amendment, 18 USC 922(g), takes care of the "banning".