Its because both Justin and Keremmeric have the same number of points, because they have the same number of points they are both technically 7th. I was tied with Inspired118 for a long time for 4th, but I eventually got another achievement so I'm now 4th and she is 5th.
That's not an accurate comparison. Of the three people, there would be two number 1's and a number 3, its the same situation here. Justin and Keremmeric are number 7 and you are number 9. You are not number 8, because there are 8 people ahead of you on the leaderboard. The number 8 position will belong to whoever is left after either Justin or Keremmeric gets another achievement. Keremmeric is probably going to be the next number 8 because he isn't as active as Justin is. Try to think of it like a decision waiting to happen; "Someone needs to be number 7 and someone needs to be number 8, but both have the same number of points. See who it is on the next episode of Achievements the Points Quest!" Honestly though dude, don't worry about it its not a big deal, you wouldn't be number 8 either way, because when Justin or Keremmeric gets an achievement you are just going to be 9 again anyway.
Well yeah, the leaderboard is entirely dependent on Achievements, so in theory, yes, that would be the case, however unlikely. Jacce has like 5,400 something points, that's 1,000 more than double my score. I don't think I could donate enough time to ever catch up with him. Its not like it really matters though, it just shows the comparison of how someone is contributing to the site, its not like its some kind of contest. In theory, if everyone would be #1 it would just be as long as a new achievement is not awarded.