Probably because he has higher than 80% IV (individual values) wich is quite good even though it has lower cp it is has better potential, so on the long run it is a better eevee. Dont know why it was transfered though, do you have an eevee with higher than 500CP? Thats probably why it got replaced, not because you have a 100CP one, the CP doesnt matter while looking for IVs.