Does arc star stun before exploding too?

Yea they do, if you get direct hit by an Arc star its more or less game over.

"After being thrown, the Arc Star sticks to surfaces and players while also dealing damage on impact. After 3 seconds, the Arc Star explodes, causing up to 70 damage to enemies and stunning them for 5 seconds. If the enemy has shields, those will be disabled entirely no matter where they are in the splash zone. The explosion's "splash" damage decreases with distance from the Arc Star itself. The explosion is able to destroy doors.

Similar to other throwables, you may hold up to two Arc Stars per inventory slot."

Source: https://apexlegends.gamepedia.com/Arc_Star

I am sure that i did not get hit by it, because after being stunned i managed to run away from it and not get the 70 damage, but the wraith i faced shredded me.

If it explodes on the ground and you're near it, you'll get stunned. If someone throws it and it successfully lands on you, your Legend will immediately get stunned prior to explosion.