In what forum did you originally post? If GD, no rule was violated; a mod simply chose to move your thread of his own will. You are in the California Hometown forum now (probably the best place to ask, though; in that sense, the mod kinda did you a favor).
Legal antiques, which include firearms that do not use fixed ammunition (such as the muzzle-loader in question), pre-1899 firearms (including cartridge firearms), and replicas of pre-1899 firearms that use cartridges not available through ordinary channels of commerce, do not require an FFL in CA. They can be bought face-to-face or be shipped directly to the recipient's address, whether the transaction is intrastate or interstate. The recipient also does not have to report it or register the firearm.
My first firearm was a muzze-loader I bought via mail-order from Cabelas when I was 11 or 12. It went right to my house. The laws here and Federally on the matter have not really changed since then.