Hextech Chest on unowned champions not given after S [CLIENT]

I don't own thresh but I just played for the very first time just now and got an S. Ge's free this week. At the end it said that I got S rank then "Congrats you got a hextech chest" (or something similar in orange letters).

I check but got no chest in Loot. Check the profile page, had 2 available chest icon before the game, still have 2. I check Thresh on champion page. The box icon is not light up. My "Season Highest Grade" is still N/A but the "Champion Points" that count towards getting mastery crest is given (from 0 to 1547)

Is this a bug or am I supposed to be punished for not owning the champion?

If this is intended then the system is very flawed. Hextech is supposed to help everybody including new players who don't own many champions. By limiting that they're only rewarded for playing champion they own, and only getting the reward once per champion, blocks them out of the hextech content after the 1st month or 2.