Your box collision probably collides with the car mesh, maybe with the landscape, hard to say without info about how you configured collisions.
Besides optimizing collision profile to not detect what it actually detects, you could use a branch. If “other actor” (on overlap event) is equal to player character, then create widget. You could also cast to the character class and create the widget if the cast succeeds, but it would react to any character coming in the box (AI or other player)