That is what it looks like to me, they are usually placed around the blacksmith's area. I used it to turn my glass daggers into fine glass daggers +2 damage.

Later, I found a potion that increases smithing 30% for 30 seconds. Would this have made a difference had I had this potion before exercise bike sharpening those glass daggers?

Or is it only for creating items?

I laughed so hard at "exercise bike".

It's called a "grindstone".

Creating items is governed by what perks you have. Improving at a workbench or grindstone are directly affected by skill, those potions, enchants, or perks boosting effectiveness for a certain item tier.

It says Grindstone when you put your cursor over it... But, yes, the potions do make sharpening better.