I'm making a homebrew race and the Lizardfolks Hunter's Lore fits perfectly with the race.

So I go to modifiers - proficiency - and the option "Choose a Lizardfolk skill" is not there.

I assumed it was because I don't own the Lizardfolk race but I can get "Choose a Centaur skill" and "Choose a Minotaur skill" and I don't own either race.

So is it a bug that I can access some but not others? If I need to own Lizardfolk then why don't I need the other two?

Edit: I also have other options I don't own, like Order domain skills for example. So this seems very arbitrary. 

That’s because “choose a Lizardfolk skill” is not a modifier subtype. Not all of the skill groups are. You can accomplish it with Options and attach each proficiency individually to its own Option. If you need it, I gave a full walkthrough on how to set up Options in the Subclasses & Races FAQ #1: (https://www.dndbeyond.com/forums/dungeons-dragons-discussion/homebrew-house-rules/131411-a-homebrewers-how-to-faq).

Thank you!