Which tooltip is that? The tooltip for Lightstepper says both.
Regardless, yes, it helps for both secrets and traps, without a doubt.
Tool over "Perception", it'll bring up the light stepper bonus and specifically says "only for trap detection".
Ah, ok. Despite the omission in the Perception attribute tooltip, it does assist with finding secrets as well as traps. This is actually specifically mentioned in the tutorial dungeon when it advises you to
"Assign points to your Perception stat to reveal traps and secrets." (in a popup-tip when you reveal and use the hidden button on the door blocking your progress).
As for Lightstepper, I happen to have a saved game point at a location in Cyseal where there is a hidden gem that can't be seen (even if you're right on top of it) unless your perception score is high enough. I have unspent talent and attribute points on that save. When I raise my perception up, I immediately discover the hidden gem. If I instead reload and put points into Lightstepper, I still immediately discover the hidden gem. So, both methods will aid in discovering secrets (and not just traps).