Most of you know that to get a hidden ability you have to catch the Pokemon in the horde with the ability or in the friend safari. I checked bulbapedia and there is no way to get a horde encounter with a group of Qwilfish or in the friend safari. it is impossible to get it a hidden ability in a wild Pokemon to my understanding so how can someone get a Qwilfish with the hidden ability?
Thanks for the help!
For a HA qwilish you will need to transfer from older version.
Hope I helped :D
I know this is old, but you can also now use the virtual player versions of GSC which defaults to the hidden ability when transferred.