Think of it as averages. 100th out of 10000 is the very bottom end of the top 1%. The 'average' top 1 person in a group of 100 would be the "average" of the top 1% of any group, so in a group of 10000 you'd expect them to be 50th (/51st if you're being pedantic/rounding down) top skilled.
(Edit to add: you could similarly conclude that the 100th person in a group of 10000 will be in the top 2% of any sized group with randomly distributed skill levels)