If a nade hits you directly, you slow down, which gives the enemy a higher change of killing you with his nade.
If the player happens to be on 1 health, you will kill him with the smokegrenade.
You lose 1 health on being hit directly with a smokegrenade.
It happens all the time that people lose 1 health because of smoke/nades.
But the change that the enemy player is having 1 health is very very rare.