I'm playing a thief on adept difficulty and today i was walking with a ebony war axe with a frost enchantment on it through the forest. I came across a frost troll and it only took a few hits and he was dead. I was completely shocked at how easy it was to kill him. Am I overpowered or was it just a good weapon?

Depends on your skills.

Sorry but I don't buy it.
A thief character is not the strongest types when it comes to tanking. Your frost enchantment is useless against it.
Even my assassin (level 71) at legendary difficulty with a Legendary daedric Dagger has trouble to survive if I don't backstabbing him.

But if you feel the game is to easy try to enter the realm of Expert difficulty or even master

I put a lot of points into the first one handed skill to increase damage 20%. And apparently frost damage does work because he didnt resist the damage.

Frost trolls are resistant to frost damage. Not sure if that translates to being immune, but still a resistance is there. Anything that is of a particular element will always be resistant or immune to it's attacks.

They have 460 HPs and no AR. So, playing on adept, a weapon dealing 100 damage will take him out in just a few hits.