[2019] "Whenever we eventually release our 145th champ, we'll increase the rotation to 15 free champs (we're rounding up)." Qiyana was #145.

Two years ago, Riot changed the free champion rotation from 10 champions to 14 champions.

https://boards.na.leagueoflegends.com/en/c/developer-corner/Exl3sEaO-expanding-the-weekly-free-champion-rotation

The plan was to make the free champion 10% of the number of champions, and this post from Cactopus explicitly says that they will round up when they get to 145. Qiyana is the 145th champion but the free rotation is still 14 champions.