They're not vanilla game rules, RobertFrans already told you that - and that's why you can't find any information about them online. Did you look at the wiki page Robert linked you?
When you type "gamerule <thing>" into chat, it will create a new custom game rule if one called <thing> doesn't already exist, just like Christy182 says (and like the wiki says) - and write it to level.dat. When you use the tab key for autocomplete options, it then reads the list of game rules back out of level.dat which is why you can see them in your screenshots.
Notice that in your screenshots you actually misspelt it "gammertags". You also have a load of duplicates where you've mistyped "keepInventory".