i got a shinyfrillish from the random swap and it has an "original owner"? I don't think that's supposed to happen.

If the pokemon you swapped, was created after the Original Owner feature was added then yes the shinyFrillish should have the owner that found it on the map.

oh but how do you put them in the random swap

you dont, Da man choose which pokemon he want in the random swap, and when people swap a pokemon one of the pokemon he chose will become that pokemon.

let say you brought a pokemon off the buy page that I sold (and was the original owner), and then you decide to takes that pokemon and swapped it for a shinies, after a few swapped it turned into a ShinyMachop, since I was the original owner of the pokemon before the swapped, it will just keep it like that,

wow thats awesome i didnt know that.