You must have used friendship, heres how Eevee evolving works, the original 3 use stones but all the others have unique methoods.
Vaporeon = Use Water Stone on Eevee
Joltoen = Use Thunder Stone on Eevee
Flareon = Use Fire Stone on Eevee
Espeon = Get high Friendship Level at DAY with Eevee
Umbreon = Get high Friendship Level at NIGHT with Eevee
(Friendship level can't really be viewed I don't think and I'm not really sure how it works)
Glaceon = Get Eevee to level up near an Ice Rock (Basically certain snowy areas)
Leafeon = Get Eevee to level up near a Moss Rock (Certain forested areas)
Sylveon = Get high Affection Level with Eevee, regardless of time (I'm not sure how it works either but I know Affection and Friendship are different stats, if you got Sylveon while trying to get the others you probably leveled up affection instead of friendship, I'm not really sure how to get either but you could probably look it up)