What is with these new champion "levels"

https://cdn.discordapp.com/attachments/548185790484840451/616488621503152138/unknown.png so i was looking at the new UI for the collection on champions, and something feels off, my champions have "levels" and i dont understand what they are for, It cant be mastery, because that doesnt align with what i show in the link, sion and other mastery 4 champs are level 7, so then what could it be? does it mean anything? Id like an explanation.
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We're testing a new feature that gives the option to view discussion comments in chronological order. Some testers have pointed out situations in which they feel a linear view could be helpful, so we'd like see how you guys make use of it.

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