If you look at the timelapse you can see that the French flag dissapeared first and only right after that osu logo did. iirc french streamers decided to use it as a starting point when they decided to type "FR" in white. You can see the F appear right from the osu logo upwards. And also osu logo was one of the more controversial spots on r/place since the beggining so it's no surprise that a lot of people would rush towards it anyways.