Does that confirm that Rinnegan users don't have to be from a specific clan to learn certain KKG ? And since all KKG come from Kaguya and Sasuke has a portion of her power, does that mean he can use ice jutsu and lava jutsu ?
Mei has the lava kekkei genkai (bloodline).
Not everyone with a kekkei genkai is in a traditional clan.
Especially for a long while in the mist village where people would be executed if they found out that you had a kekkei genkai.
Even different villages can have the same kekkei genkai.
Some examples:
Lava release is seen in both Kumogakure, Iwagakure and Kirigakure.
Magnet release is seen in both Sunagakure and Kumogakure.
In the episodes where Sasuke eventually battles that girl from the Chinoike clan, there are a lot of kekkei genkai users in that colisium where they bet on fighters. In En Oyashiro his group was also a Lava release user and that group was made of people with kekkei genkai.